diff --git a/contrib/llvm-project/libcxx/include/type_traits b/contrib/llvm-project/libcxx/include/type_traits
index 3391999675a0..daf031e475f7 100644
--- a/contrib/llvm-project/libcxx/include/type_traits
+++ b/contrib/llvm-project/libcxx/include/type_traits
@@ -1,4155 +1,4155 @@
 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP_TYPE_TRAITS
 #define _LIBCPP_TYPE_TRAITS
 
 /*
     type_traits synopsis
 
 namespace std
 {
 
     // helper class:
     template <class T, T v> struct integral_constant;
     typedef integral_constant<bool, true>  true_type;   // C++11
     typedef integral_constant<bool, false> false_type;  // C++11
 
     template <bool B>                                   // C++14
     using bool_constant = integral_constant<bool, B>;   // C++14
     typedef bool_constant<true> true_type;              // C++14
     typedef bool_constant<false> false_type;            // C++14
 
     // helper traits
     template <bool, class T = void> struct enable_if;
     template <bool, class T, class F> struct conditional;
 
     // Primary classification traits:
     template <class T> struct is_void;
     template <class T> struct is_null_pointer;  // C++14
     template <class T> struct is_integral;
     template <class T> struct is_floating_point;
     template <class T> struct is_array;
     template <class T> struct is_pointer;
     template <class T> struct is_lvalue_reference;
     template <class T> struct is_rvalue_reference;
     template <class T> struct is_member_object_pointer;
     template <class T> struct is_member_function_pointer;
     template <class T> struct is_enum;
     template <class T> struct is_union;
     template <class T> struct is_class;
     template <class T> struct is_function;
 
     // Secondary classification traits:
     template <class T> struct is_reference;
     template <class T> struct is_arithmetic;
     template <class T> struct is_fundamental;
     template <class T> struct is_member_pointer;
     template <class T> struct is_scoped_enum; // C++2b
     template <class T> struct is_scalar;
     template <class T> struct is_object;
     template <class T> struct is_compound;
 
     // Const-volatile properties and transformations:
     template <class T> struct is_const;
     template <class T> struct is_volatile;
     template <class T> struct remove_const;
     template <class T> struct remove_volatile;
     template <class T> struct remove_cv;
     template <class T> struct add_const;
     template <class T> struct add_volatile;
     template <class T> struct add_cv;
 
     // Reference transformations:
     template <class T> struct remove_reference;
     template <class T> struct add_lvalue_reference;
     template <class T> struct add_rvalue_reference;
 
     // Pointer transformations:
     template <class T> struct remove_pointer;
     template <class T> struct add_pointer;
 
     template<class T> struct type_identity;                     // C++20
     template<class T>
       using type_identity_t = typename type_identity<T>::type;  // C++20
 
     // Integral properties:
     template <class T> struct is_signed;
     template <class T> struct is_unsigned;
     template <class T> struct make_signed;
     template <class T> struct make_unsigned;
 
     // Array properties and transformations:
     template <class T> struct rank;
     template <class T, unsigned I = 0> struct extent;
     template <class T> struct remove_extent;
     template <class T> struct remove_all_extents;
 
     template <class T> struct is_bounded_array;                 // C++20
     template <class T> struct is_unbounded_array;               // C++20
 
     // Member introspection:
     template <class T> struct is_pod;
     template <class T> struct is_trivial;
     template <class T> struct is_trivially_copyable;
     template <class T> struct is_standard_layout;
     template <class T> struct is_literal_type; // Deprecated in C++17; removed in C++20
     template <class T> struct is_empty;
     template <class T> struct is_polymorphic;
     template <class T> struct is_abstract;
     template <class T> struct is_final; // C++14
     template <class T> struct is_aggregate; // C++17
 
     template <class T, class... Args> struct is_constructible;
     template <class T>                struct is_default_constructible;
     template <class T>                struct is_copy_constructible;
     template <class T>                struct is_move_constructible;
     template <class T, class U>       struct is_assignable;
     template <class T>                struct is_copy_assignable;
     template <class T>                struct is_move_assignable;
     template <class T, class U>       struct is_swappable_with;       // C++17
     template <class T>                struct is_swappable;            // C++17
     template <class T>                struct is_destructible;
 
     template <class T, class... Args> struct is_trivially_constructible;
     template <class T>                struct is_trivially_default_constructible;
     template <class T>                struct is_trivially_copy_constructible;
     template <class T>                struct is_trivially_move_constructible;
     template <class T, class U>       struct is_trivially_assignable;
     template <class T>                struct is_trivially_copy_assignable;
     template <class T>                struct is_trivially_move_assignable;
     template <class T>                struct is_trivially_destructible;
 
     template <class T, class... Args> struct is_nothrow_constructible;
     template <class T>                struct is_nothrow_default_constructible;
     template <class T>                struct is_nothrow_copy_constructible;
     template <class T>                struct is_nothrow_move_constructible;
     template <class T, class U>       struct is_nothrow_assignable;
     template <class T>                struct is_nothrow_copy_assignable;
     template <class T>                struct is_nothrow_move_assignable;
     template <class T, class U>       struct is_nothrow_swappable_with; // C++17
     template <class T>                struct is_nothrow_swappable;      // C++17
     template <class T>                struct is_nothrow_destructible;
 
     template <class T> struct has_virtual_destructor;
 
     template<class T> struct has_unique_object_representations;         // C++17
 
     // Relationships between types:
     template <class T, class U> struct is_same;
     template <class Base, class Derived> struct is_base_of;
 
     template <class From, class To> struct is_convertible;
     template <typename From, typename To> struct is_nothrow_convertible;                  // C++20
     template <typename From, typename To> inline constexpr bool is_nothrow_convertible_v; // C++20
 
     template <class Fn, class... ArgTypes> struct is_invocable;
     template <class R, class Fn, class... ArgTypes> struct is_invocable_r;
 
     template <class Fn, class... ArgTypes> struct is_nothrow_invocable;
     template <class R, class Fn, class... ArgTypes> struct is_nothrow_invocable_r;
 
     // Alignment properties and transformations:
     template <class T> struct alignment_of;
     template <size_t Len, size_t Align = most_stringent_alignment_requirement>
         struct aligned_storage;
     template <size_t Len, class... Types> struct aligned_union;
     template <class T> struct remove_cvref; // C++20
 
     template <class T> struct decay;
     template <class... T> struct common_type;
     template <class T> struct underlying_type;
     template <class> class result_of; // undefined; deprecated in C++17; removed in C++20
     template <class Fn, class... ArgTypes> class result_of<Fn(ArgTypes...)>; // deprecated in C++17; removed in C++20
     template <class Fn, class... ArgTypes> struct invoke_result;  // C++17
 
     // const-volatile modifications:
     template <class T>
       using remove_const_t    = typename remove_const<T>::type;  // C++14
     template <class T>
       using remove_volatile_t = typename remove_volatile<T>::type;  // C++14
     template <class T>
       using remove_cv_t       = typename remove_cv<T>::type;  // C++14
     template <class T>
       using add_const_t       = typename add_const<T>::type;  // C++14
     template <class T>
       using add_volatile_t    = typename add_volatile<T>::type;  // C++14
     template <class T>
       using add_cv_t          = typename add_cv<T>::type;  // C++14
 
     // reference modifications:
     template <class T>
       using remove_reference_t     = typename remove_reference<T>::type;  // C++14
     template <class T>
       using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;  // C++14
     template <class T>
       using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;  // C++14
 
     // sign modifications:
     template <class T>
       using make_signed_t   = typename make_signed<T>::type;  // C++14
     template <class T>
       using make_unsigned_t = typename make_unsigned<T>::type;  // C++14
 
     // array modifications:
     template <class T>
       using remove_extent_t      = typename remove_extent<T>::type;  // C++14
     template <class T>
       using remove_all_extents_t = typename remove_all_extents<T>::type;  // C++14
 
     template <class T>
       inline constexpr bool is_bounded_array_v
         = is_bounded_array<T>::value;                                     // C++20
       inline constexpr bool is_unbounded_array_v
         = is_unbounded_array<T>::value;                                   // C++20
 
     // pointer modifications:
     template <class T>
       using remove_pointer_t = typename remove_pointer<T>::type;  // C++14
     template <class T>
       using add_pointer_t    = typename add_pointer<T>::type;  // C++14
 
     // other transformations:
     template <size_t Len, size_t Align=default-alignment>
       using aligned_storage_t = typename aligned_storage<Len,Align>::type;  // C++14
     template <size_t Len, class... Types>
       using aligned_union_t   = typename aligned_union<Len,Types...>::type;  // C++14
     template <class T>
       using remove_cvref_t    = typename remove_cvref<T>::type;  // C++20
     template <class T>
       using decay_t           = typename decay<T>::type;  // C++14
     template <bool b, class T=void>
       using enable_if_t       = typename enable_if<b,T>::type;  // C++14
     template <bool b, class T, class F>
       using conditional_t     = typename conditional<b,T,F>::type;  // C++14
     template <class... T>
       using common_type_t     = typename common_type<T...>::type;  // C++14
     template <class T>
       using underlying_type_t = typename underlying_type<T>::type;  // C++14
     template <class T>
       using result_of_t       = typename result_of<T>::type;  // C++14; deprecated in C++17; removed in C++20
     template <class Fn, class... ArgTypes>
       using invoke_result_t   = typename invoke_result<Fn, ArgTypes...>::type;  // C++17
 
     template <class...>
       using void_t = void;   // C++17
 
       // See C++14 20.10.4.1, primary type categories
       template <class T> inline constexpr bool is_void_v
         = is_void<T>::value;                                             // C++17
       template <class T> inline constexpr bool is_null_pointer_v
         = is_null_pointer<T>::value;                                     // C++17
       template <class T> inline constexpr bool is_integral_v
         = is_integral<T>::value;                                         // C++17
       template <class T> inline constexpr bool is_floating_point_v
         = is_floating_point<T>::value;                                   // C++17
       template <class T> inline constexpr bool is_array_v
         = is_array<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_pointer_v
         = is_pointer<T>::value;                                          // C++17
       template <class T> inline constexpr bool is_lvalue_reference_v
         = is_lvalue_reference<T>::value;                                 // C++17
       template <class T> inline constexpr bool is_rvalue_reference_v
         = is_rvalue_reference<T>::value;                                 // C++17
       template <class T> inline constexpr bool is_member_object_pointer_v
         = is_member_object_pointer<T>::value;                            // C++17
       template <class T> inline constexpr bool is_member_function_pointer_v
         = is_member_function_pointer<T>::value;                          // C++17
       template <class T> inline constexpr bool is_enum_v
         = is_enum<T>::value;                                             // C++17
       template <class T> inline constexpr bool is_union_v
         = is_union<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_class_v
         = is_class<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_function_v
         = is_function<T>::value;                                         // C++17
 
       // See C++14 20.10.4.2, composite type categories
       template <class T> inline constexpr bool is_reference_v
         = is_reference<T>::value;                                        // C++17
       template <class T> inline constexpr bool is_arithmetic_v
         = is_arithmetic<T>::value;                                       // C++17
       template <class T> inline constexpr bool is_fundamental_v
         = is_fundamental<T>::value;                                      // C++17
       template <class T> inline constexpr bool is_object_v
         = is_object<T>::value;                                           // C++17
       template <class T> inline constexpr bool is_scalar_v
         = is_scalar<T>::value;                                           // C++17
       template <class T> inline constexpr bool is_compound_v
         = is_compound<T>::value;                                         // C++17
       template <class T> inline constexpr bool is_member_pointer_v
         = is_member_pointer<T>::value;                                   // C++17
       template <class T> inline constexpr bool is_scoped_enum_v
         = is_scoped_enum<T>::value;                                      // C++2b
 
       // See C++14 20.10.4.3, type properties
       template <class T> inline constexpr bool is_const_v
         = is_const<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_volatile_v
         = is_volatile<T>::value;                                         // C++17
       template <class T> inline constexpr bool is_trivial_v
         = is_trivial<T>::value;                                          // C++17
       template <class T> inline constexpr bool is_trivially_copyable_v
         = is_trivially_copyable<T>::value;                               // C++17
       template <class T> inline constexpr bool is_standard_layout_v
         = is_standard_layout<T>::value;                                  // C++17
       template <class T> inline constexpr bool is_pod_v
         = is_pod<T>::value;                                              // C++17
       template <class T> inline constexpr bool is_literal_type_v
         = is_literal_type<T>::value;                                     // C++17; deprecated in C++17; removed in C++20
       template <class T> inline constexpr bool is_empty_v
         = is_empty<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_polymorphic_v
         = is_polymorphic<T>::value;                                      // C++17
       template <class T> inline constexpr bool is_abstract_v
         = is_abstract<T>::value;                                         // C++17
       template <class T> inline constexpr bool is_final_v
         = is_final<T>::value;                                            // C++17
       template <class T> inline constexpr bool is_aggregate_v
         = is_aggregate<T>::value;                                        // C++17
       template <class T> inline constexpr bool is_signed_v
         = is_signed<T>::value;                                           // C++17
       template <class T> inline constexpr bool is_unsigned_v
         = is_unsigned<T>::value;                                         // C++17
       template <class T, class... Args> inline constexpr bool is_constructible_v
         = is_constructible<T, Args...>::value;                           // C++17
       template <class T> inline constexpr bool is_default_constructible_v
         = is_default_constructible<T>::value;                            // C++17
       template <class T> inline constexpr bool is_copy_constructible_v
         = is_copy_constructible<T>::value;                               // C++17
       template <class T> inline constexpr bool is_move_constructible_v
         = is_move_constructible<T>::value;                               // C++17
       template <class T, class U> inline constexpr bool is_assignable_v
         = is_assignable<T, U>::value;                                    // C++17
       template <class T> inline constexpr bool is_copy_assignable_v
         = is_copy_assignable<T>::value;                                  // C++17
       template <class T> inline constexpr bool is_move_assignable_v
         = is_move_assignable<T>::value;                                  // C++17
       template <class T, class U> inline constexpr bool is_swappable_with_v
         = is_swappable_with<T, U>::value;                                // C++17
       template <class T> inline constexpr bool is_swappable_v
         = is_swappable<T>::value;                                        // C++17
       template <class T> inline constexpr bool is_destructible_v
         = is_destructible<T>::value;                                     // C++17
       template <class T, class... Args> inline constexpr bool is_trivially_constructible_v
         = is_trivially_constructible<T, Args...>::value;                 // C++17
       template <class T> inline constexpr bool is_trivially_default_constructible_v
         = is_trivially_default_constructible<T>::value;                  // C++17
       template <class T> inline constexpr bool is_trivially_copy_constructible_v
         = is_trivially_copy_constructible<T>::value;                     // C++17
       template <class T> inline constexpr bool is_trivially_move_constructible_v
         = is_trivially_move_constructible<T>::value;                     // C++17
       template <class T, class U> inline constexpr bool is_trivially_assignable_v
         = is_trivially_assignable<T, U>::value;                          // C++17
       template <class T> inline constexpr bool is_trivially_copy_assignable_v
         = is_trivially_copy_assignable<T>::value;                        // C++17
       template <class T> inline constexpr bool is_trivially_move_assignable_v
         = is_trivially_move_assignable<T>::value;                        // C++17
       template <class T> inline constexpr bool is_trivially_destructible_v
         = is_trivially_destructible<T>::value;                           // C++17
       template <class T, class... Args> inline constexpr bool is_nothrow_constructible_v
         = is_nothrow_constructible<T, Args...>::value;                   // C++17
       template <class T> inline constexpr bool is_nothrow_default_constructible_v
         = is_nothrow_default_constructible<T>::value;                    // C++17
       template <class T> inline constexpr bool is_nothrow_copy_constructible_v
         = is_nothrow_copy_constructible<T>::value;                       // C++17
       template <class T> inline constexpr bool is_nothrow_move_constructible_v
         = is_nothrow_move_constructible<T>::value;                       // C++17
       template <class T, class U> inline constexpr bool is_nothrow_assignable_v
         = is_nothrow_assignable<T, U>::value;                            // C++17
       template <class T> inline constexpr bool is_nothrow_copy_assignable_v
         = is_nothrow_copy_assignable<T>::value;                          // C++17
       template <class T> inline constexpr bool is_nothrow_move_assignable_v
         = is_nothrow_move_assignable<T>::value;                          // C++17
       template <class T, class U> inline constexpr bool is_nothrow_swappable_with_v
         = is_nothrow_swappable_with<T, U>::value;                       // C++17
       template <class T> inline constexpr bool is_nothrow_swappable_v
         = is_nothrow_swappable<T>::value;                               // C++17
       template <class T> inline constexpr bool is_nothrow_destructible_v
         = is_nothrow_destructible<T>::value;                             // C++17
       template <class T> inline constexpr bool has_virtual_destructor_v
         = has_virtual_destructor<T>::value;                              // C++17
       template<class T> inline constexpr bool has_unique_object_representations_v // C++17
         = has_unique_object_representations<T>::value;
 
       // See C++14 20.10.5, type property queries
       template <class T> inline constexpr size_t alignment_of_v
         = alignment_of<T>::value;                                        // C++17
       template <class T> inline constexpr size_t rank_v
         = rank<T>::value;                                                // C++17
       template <class T, unsigned I = 0> inline constexpr size_t extent_v
         = extent<T, I>::value;                                           // C++17
 
       // See C++14 20.10.6, type relations
       template <class T, class U> inline constexpr bool is_same_v
         = is_same<T, U>::value;                                          // C++17
       template <class Base, class Derived> inline constexpr bool is_base_of_v
         = is_base_of<Base, Derived>::value;                              // C++17
       template <class From, class To> inline constexpr bool is_convertible_v
         = is_convertible<From, To>::value;                               // C++17
       template <class Fn, class... ArgTypes> inline constexpr bool is_invocable_v
         = is_invocable<Fn, ArgTypes...>::value;                          // C++17
       template <class R, class Fn, class... ArgTypes> inline constexpr bool is_invocable_r_v
         = is_invocable_r<R, Fn, ArgTypes...>::value;                     // C++17
       template <class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_v
         = is_nothrow_invocable<Fn, ArgTypes...>::value;                  // C++17
       template <class R, class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_r_v
         = is_nothrow_invocable_r<R, Fn, ArgTypes...>::value;             // C++17
 
       // [meta.logical], logical operator traits:
       template<class... B> struct conjunction;                           // C++17
       template<class... B>
         inline constexpr bool conjunction_v = conjunction<B...>::value;  // C++17
       template<class... B> struct disjunction;                           // C++17
       template<class... B>
         inline constexpr bool disjunction_v = disjunction<B...>::value;  // C++17
       template<class B> struct negation;                                 // C++17
       template<class B>
         inline constexpr bool negation_v = negation<B>::value;           // C++17
 
 }
 
 */
 #include <__config>
 #include <cstddef>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS pair;
 template <class _Tp> class _LIBCPP_TEMPLATE_VIS reference_wrapper;
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash;
 
 template <class _Tp, _Tp __v>
 struct _LIBCPP_TEMPLATE_VIS integral_constant
 {
   static _LIBCPP_CONSTEXPR const _Tp      value = __v;
   typedef _Tp               value_type;
   typedef integral_constant type;
   _LIBCPP_INLINE_VISIBILITY
   _LIBCPP_CONSTEXPR operator value_type() const _NOEXCEPT {return value;}
 #if _LIBCPP_STD_VER > 11
   _LIBCPP_INLINE_VISIBILITY
   constexpr value_type operator ()() const _NOEXCEPT {return value;}
 #endif
 };
 
 template <class _Tp, _Tp __v>
 _LIBCPP_CONSTEXPR const _Tp integral_constant<_Tp, __v>::value;
 
 #if _LIBCPP_STD_VER > 14
 template <bool __b>
 using bool_constant = integral_constant<bool, __b>;
 #define _LIBCPP_BOOL_CONSTANT(__b) bool_constant<(__b)>
 #else
 #define _LIBCPP_BOOL_CONSTANT(__b) integral_constant<bool,(__b)>
 #endif
 
 template <bool, class _Tp = void> struct _LIBCPP_TEMPLATE_VIS enable_if {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS enable_if<true, _Tp> {typedef _Tp type;};
 
 template <bool _Bp, class _Tp = void> using __enable_if_t _LIBCPP_NODEBUG = typename enable_if<_Bp, _Tp>::type;
 
 #if _LIBCPP_STD_VER > 11
 template <bool _Bp, class _Tp = void> using enable_if_t = typename enable_if<_Bp, _Tp>::type;
 #endif
 
 typedef _LIBCPP_BOOL_CONSTANT(true)  true_type;
 typedef _LIBCPP_BOOL_CONSTANT(false) false_type;
 
 template <bool _Val>
 using _BoolConstant _LIBCPP_NODEBUG = integral_constant<bool, _Val>;
 
 template <bool> struct _MetaBase;
 template <>
 struct _MetaBase<true> {
   template <class _Tp, class _Up>
   using _SelectImpl _LIBCPP_NODEBUG = _Tp;
   template <template <class...> class _FirstFn, template <class...> class, class ..._Args>
   using _SelectApplyImpl _LIBCPP_NODEBUG = _FirstFn<_Args...>;
   template <class _First, class...>
   using _FirstImpl _LIBCPP_NODEBUG = _First;
   template <class, class _Second, class...>
   using _SecondImpl _LIBCPP_NODEBUG = _Second;
   template <class _Result, class _First, class ..._Rest>
   using _OrImpl _LIBCPP_NODEBUG = typename _MetaBase<_First::value != true && sizeof...(_Rest) != 0>::template _OrImpl<_First, _Rest...>;
 };
 
 template <>
 struct _MetaBase<false> {
   template <class _Tp, class _Up>
   using _SelectImpl _LIBCPP_NODEBUG = _Up;
   template <template <class...> class, template <class...> class _SecondFn, class ..._Args>
   using _SelectApplyImpl _LIBCPP_NODEBUG = _SecondFn<_Args...>;
   template <class _Result, class ...>
   using _OrImpl _LIBCPP_NODEBUG = _Result;
 };
 template <bool _Cond, class _IfRes, class _ElseRes>
 using _If _LIBCPP_NODEBUG = typename _MetaBase<_Cond>::template _SelectImpl<_IfRes, _ElseRes>;
 template <class ..._Rest>
 using _Or _LIBCPP_NODEBUG = typename _MetaBase< sizeof...(_Rest) != 0 >::template _OrImpl<false_type, _Rest...>;
 template <class _Pred>
 struct _Not : _BoolConstant<!_Pred::value> {};
 template <class ..._Args>
 using _FirstType _LIBCPP_NODEBUG = typename _MetaBase<(sizeof...(_Args) >= 1)>::template _FirstImpl<_Args...>;
 template <class ..._Args>
 using _SecondType _LIBCPP_NODEBUG = typename _MetaBase<(sizeof...(_Args) >= 2)>::template _SecondImpl<_Args...>;
 
 template <class ...> using __expand_to_true = true_type;
 template <class ..._Pred>
 __expand_to_true<__enable_if_t<_Pred::value>...> __and_helper(int);
 template <class ...>
 false_type __and_helper(...);
 template <class ..._Pred>
 using _And _LIBCPP_NODEBUG = decltype(__and_helper<_Pred...>(0));
 
 template <template <class...> class _Func, class ..._Args>
 struct _Lazy : _Func<_Args...> {};
 
 // Member detector base
 
 template <template <class...> class _Templ, class ..._Args, class = _Templ<_Args...> >
 true_type __sfinae_test_impl(int);
 template <template <class...> class, class ...>
 false_type __sfinae_test_impl(...);
 
 template <template <class ...> class _Templ, class ..._Args>
 using _IsValidExpansion _LIBCPP_NODEBUG = decltype(__sfinae_test_impl<_Templ, _Args...>(0));
 
 template <class>
 struct __void_t { typedef void type; };
 
 template <class _Tp>
 struct __identity { typedef _Tp type; };
 
 template <class _Tp>
 using __identity_t _LIBCPP_NODEBUG = typename __identity<_Tp>::type;
 
 template <class _Tp, bool>
 struct _LIBCPP_TEMPLATE_VIS __dependent_type : public _Tp {};
 
 
 template <bool _Bp, class _If, class _Then>
     struct _LIBCPP_TEMPLATE_VIS conditional {typedef _If type;};
 template <class _If, class _Then>
     struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> {typedef _Then type;};
 
 #if _LIBCPP_STD_VER > 11
 template <bool _Bp, class _If, class _Then> using conditional_t = typename conditional<_Bp, _If, _Then>::type;
 #endif
 
 // is_same
 
 template <class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS is_same : _BoolConstant<__is_same(_Tp, _Up)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class _Up>
 inline constexpr bool is_same_v = __is_same(_Tp, _Up);
 #endif
 
 // _IsSame<T,U> has the same effect as is_same<T,U> but instantiates fewer types:
 // is_same<A,B> and is_same<C,D> are guaranteed to be different types, but
 // _IsSame<A,B> and _IsSame<C,D> are the same type (namely, false_type).
 // Neither GCC nor Clang can mangle the __is_same builtin, so _IsSame
 // mustn't be directly used anywhere that contributes to name-mangling
 // (such as in a dependent return type).
 
 template <class _Tp, class _Up>
 using _IsSame = _BoolConstant<__is_same(_Tp, _Up)>;
 
 template <class _Tp, class _Up>
 using _IsNotSame = _BoolConstant<!__is_same(_Tp, _Up)>;
 
 template <class _Tp>
 using __test_for_primary_template = __enable_if_t<
     _IsSame<_Tp, typename _Tp::__primary_template>::value
   >;
 template <class _Tp>
 using __is_primary_template = _IsValidExpansion<
     __test_for_primary_template, _Tp
   >;
 
 // helper class
 
 struct __two {char __lx[2];};
 
 // is_const
 
 #if __has_keyword(__is_const)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_const : _BoolConstant<__is_const(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_const_v = __is_const(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_const            : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_const<_Tp const> : public true_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_const_v = is_const<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_const)
 
 // is_volatile
 
 #if __has_keyword(__is_volatile)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_volatile : _BoolConstant<__is_volatile(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_volatile_v = __is_volatile(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_volatile               : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_volatile<_Tp volatile> : public true_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_volatile_v = is_volatile<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_volatile)
 
 // remove_const
 
 #if __has_keyword(__remove_const)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS remove_const {typedef __remove_const(_Tp) type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_const_t = __remove_const(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_const            {typedef _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_const<const _Tp> {typedef _Tp type;};
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_const_t = typename remove_const<_Tp>::type;
 #endif
 
 #endif // __has_keyword(__remove_const)
 
 // remove_volatile
 
 #if __has_keyword(__remove_volatile)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS remove_volatile {typedef __remove_volatile(_Tp) type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_volatile_t = __remove_volatile(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_volatile               {typedef _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_volatile<volatile _Tp> {typedef _Tp type;};
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_volatile_t = typename remove_volatile<_Tp>::type;
 #endif
 
 #endif // __has_keyword(__remove_volatile)
 
 // remove_cv
 
 #if __has_keyword(__remove_cv)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS remove_cv {typedef __remove_cv(_Tp) type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_cv_t = __remove_cv(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_cv
 {typedef typename remove_volatile<typename remove_const<_Tp>::type>::type type;};
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_cv_t = typename remove_cv<_Tp>::type;
 #endif
 
 #endif // __has_keyword(__remove_cv)
 
 // is_void
 
 #if __has_keyword(__is_void)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_void : _BoolConstant<__is_void(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_void_v = __is_void(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_void
     : public is_same<typename remove_cv<_Tp>::type, void> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_void_v = is_void<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_void)
 
 // __is_nullptr_t
 
 template <class _Tp> struct __is_nullptr_t_impl       : public false_type {};
 template <>          struct __is_nullptr_t_impl<nullptr_t> : public true_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS __is_nullptr_t
     : public __is_nullptr_t_impl<typename remove_cv<_Tp>::type> {};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_null_pointer
     : public __is_nullptr_t_impl<typename remove_cv<_Tp>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_null_pointer_v = is_null_pointer<_Tp>::value;
 #endif
 #endif // _LIBCPP_STD_VER > 11
 
 // is_integral
 
 #if __has_keyword(__is_integral)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_integral : _BoolConstant<__is_integral(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_integral_v = __is_integral(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_integral
     : public _BoolConstant<__libcpp_is_integral<typename remove_cv<_Tp>::type>::value> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_integral_v = is_integral<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_integral)
 
 // [basic.fundamental] defines five standard signed integer types;
 // __int128_t is an extended signed integer type.
 // The signed and unsigned integer types, plus bool and the
 // five types with "char" in their name, compose the "integral" types.
 
 template <class _Tp> struct __libcpp_is_signed_integer : public false_type {};
 template <> struct __libcpp_is_signed_integer<signed char>      : public true_type {};
 template <> struct __libcpp_is_signed_integer<signed short>     : public true_type {};
 template <> struct __libcpp_is_signed_integer<signed int>       : public true_type {};
 template <> struct __libcpp_is_signed_integer<signed long>      : public true_type {};
 template <> struct __libcpp_is_signed_integer<signed long long> : public true_type {};
 #ifndef _LIBCPP_HAS_NO_INT128
 template <> struct __libcpp_is_signed_integer<__int128_t>       : public true_type {};
 #endif
 
 template <class _Tp> struct __libcpp_is_unsigned_integer : public false_type {};
 template <> struct __libcpp_is_unsigned_integer<unsigned char>      : public true_type {};
 template <> struct __libcpp_is_unsigned_integer<unsigned short>     : public true_type {};
 template <> struct __libcpp_is_unsigned_integer<unsigned int>       : public true_type {};
 template <> struct __libcpp_is_unsigned_integer<unsigned long>      : public true_type {};
 template <> struct __libcpp_is_unsigned_integer<unsigned long long> : public true_type {};
 #ifndef _LIBCPP_HAS_NO_INT128
 template <> struct __libcpp_is_unsigned_integer<__uint128_t>        : public true_type {};
 #endif
 
 // is_floating_point
 // <concepts> implements __libcpp_floating_point
 
 template <class _Tp> struct __libcpp_is_floating_point              : public false_type {};
 template <>          struct __libcpp_is_floating_point<float>       : public true_type {};
 template <>          struct __libcpp_is_floating_point<double>      : public true_type {};
 template <>          struct __libcpp_is_floating_point<long double> : public true_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_floating_point
     : public __libcpp_is_floating_point<typename remove_cv<_Tp>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_floating_point_v = is_floating_point<_Tp>::value;
 #endif
 
 // is_array
 
 #if __has_keyword(__is_array)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_array : _BoolConstant<__is_array(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_array_v = __is_array(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_array
     : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_array<_Tp[]>
     : public true_type {};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS is_array<_Tp[_Np]>
     : public true_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_array_v = is_array<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_array)
 
 // is_pointer
 
 // Before AppleClang 12.0.5, __is_pointer didn't work for Objective-C types.
 #if __has_keyword(__is_pointer) &&                                             \
     !(defined(_LIBCPP_APPLE_CLANG_VER) && _LIBCPP_APPLE_CLANG_VER < 1205)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_pointer : _BoolConstant<__is_pointer(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_pointer_v = __is_pointer(_Tp);
 #endif
 
 #else // __has_keyword(__is_pointer)
 
 template <class _Tp> struct __libcpp_is_pointer       : public false_type {};
 template <class _Tp> struct __libcpp_is_pointer<_Tp*> : public true_type {};
 
 template <class _Tp> struct __libcpp_remove_objc_qualifiers { typedef _Tp type; };
 #if defined(_LIBCPP_HAS_OBJC_ARC)
 template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __strong> { typedef _Tp type; };
 template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __weak> { typedef _Tp type; };
 template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __autoreleasing> { typedef _Tp type; };
 template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __unsafe_unretained> { typedef _Tp type; };
 #endif
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pointer
     : public __libcpp_is_pointer<typename __libcpp_remove_objc_qualifiers<typename remove_cv<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_pointer_v = is_pointer<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_pointer)
 
 // is_reference
 
 #if __has_keyword(__is_lvalue_reference) && \
     __has_keyword(__is_rvalue_reference) && \
     __has_keyword(__is_reference)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference : _BoolConstant<__is_lvalue_reference(_Tp)> { };
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference : _BoolConstant<__is_rvalue_reference(_Tp)> { };
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_reference : _BoolConstant<__is_reference(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_reference_v = __is_reference(_Tp);
 template <class _Tp>
 inline constexpr bool is_lvalue_reference_v = __is_lvalue_reference(_Tp);
 template <class _Tp>
 inline constexpr bool is_rvalue_reference_v = __is_rvalue_reference(_Tp);
 #endif
 
 #else // __has_keyword(__is_lvalue_reference) && etc...
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference       : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference<_Tp&> : public true_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference        : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference<_Tp&&> : public true_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference        : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference<_Tp&>  : public true_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference<_Tp&&> : public true_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_reference_v = is_reference<_Tp>::value;
 
 template <class _Tp>
 inline constexpr bool is_lvalue_reference_v = is_lvalue_reference<_Tp>::value;
 
 template <class _Tp>
 inline constexpr bool is_rvalue_reference_v = is_rvalue_reference<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_lvalue_reference) && etc...
 
 // is_union
 
 #if __has_feature(is_union) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_union
     : public integral_constant<bool, __is_union(_Tp)> {};
 
 #else
 
 template <class _Tp> struct __libcpp_union : public false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_union
     : public __libcpp_union<typename remove_cv<_Tp>::type> {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_union_v = is_union<_Tp>::value;
 #endif
 
 // is_class
 
 #if __has_feature(is_class) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_class
     : public integral_constant<bool, __is_class(_Tp)> {};
 
 #else
 
 namespace __is_class_imp
 {
 template <class _Tp> char  __test(int _Tp::*);
 template <class _Tp> __two __test(...);
 }
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_class
     : public integral_constant<bool, sizeof(__is_class_imp::__test<_Tp>(0)) == 1 && !is_union<_Tp>::value> {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_class_v = is_class<_Tp>::value;
 #endif
 
 // is_function
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_function
     : public _BoolConstant<
 #ifdef __clang__
     __is_function(_Tp)
 #else
  !(is_reference<_Tp>::value || is_const<const _Tp>::value)
 #endif
     > {};
 
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_function_v = is_function<_Tp>::value;
 #endif
 
 template <class _Tp> struct __libcpp_is_member_pointer {
   enum {
     __is_member = false,
     __is_func = false,
     __is_obj = false
   };
 };
 template <class _Tp, class _Up> struct __libcpp_is_member_pointer<_Tp _Up::*> {
   enum {
     __is_member = true,
     __is_func = is_function<_Tp>::value,
     __is_obj = !__is_func,
   };
 };
 
 #if __has_keyword(__is_member_function_pointer)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_member_function_pointer
     : _BoolConstant<__is_member_function_pointer(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_function_pointer_v = __is_member_function_pointer(_Tp);
 #endif
 
 #else // __has_keyword(__is_member_function_pointer)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_function_pointer
     : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_func > {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_function_pointer_v = is_member_function_pointer<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_member_function_pointer)
 
 // is_member_pointer
 
 #if __has_keyword(__is_member_pointer)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_member_pointer : _BoolConstant<__is_member_pointer(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_pointer_v = __is_member_pointer(_Tp);
 #endif
 
 #else // __has_keyword(__is_member_pointer)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_pointer
  : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_member > {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_pointer_v = is_member_pointer<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_member_pointer)
 
 // is_member_object_pointer
 
 #if __has_keyword(__is_member_object_pointer)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_member_object_pointer
     : _BoolConstant<__is_member_object_pointer(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_object_pointer_v = __is_member_object_pointer(_Tp);
 #endif
 
 #else // __has_keyword(__is_member_object_pointer)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_object_pointer
     : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_obj >  {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_member_object_pointer_v = is_member_object_pointer<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_member_object_pointer)
 
 // is_enum
 
 #if __has_feature(is_enum) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_enum
     : public integral_constant<bool, __is_enum(_Tp)> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_enum_v = __is_enum(_Tp);
 #endif
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_enum
     : public integral_constant<bool, !is_void<_Tp>::value             &&
                                      !is_integral<_Tp>::value         &&
                                      !is_floating_point<_Tp>::value   &&
                                      !is_array<_Tp>::value            &&
                                      !is_pointer<_Tp>::value          &&
                                      !is_reference<_Tp>::value        &&
                                      !is_member_pointer<_Tp>::value   &&
                                      !is_union<_Tp>::value            &&
                                      !is_class<_Tp>::value            &&
                                      !is_function<_Tp>::value         > {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_enum_v = is_enum<_Tp>::value;
 #endif
 
 #endif // __has_feature(is_enum) || defined(_LIBCPP_COMPILER_GCC)
 
 // is_arithmetic
 
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_arithmetic
     : public integral_constant<bool, is_integral<_Tp>::value      ||
                                      is_floating_point<_Tp>::value> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
 #endif
 
 // is_fundamental
 
 // Before Clang 10, __is_fundamental didn't work for nullptr_t.
 // In C++03 nullptr_t is library-provided but must still count as "fundamental."
 #if __has_keyword(__is_fundamental) &&                                         \
     !(defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER < 1000) &&               \
     !defined(_LIBCPP_CXX03_LANG)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_fundamental : _BoolConstant<__is_fundamental(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_fundamental_v = __is_fundamental(_Tp);
 #endif
 
 #else // __has_keyword(__is_fundamental)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_fundamental
     : public integral_constant<bool, is_void<_Tp>::value        ||
                                      __is_nullptr_t<_Tp>::value ||
                                      is_arithmetic<_Tp>::value> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_fundamental)
 
 // is_scalar
 
 // In C++03 nullptr_t is library-provided but must still count as "scalar."
 #if __has_keyword(__is_scalar) && !defined(_LIBCPP_CXX03_LANG)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_scalar : _BoolConstant<__is_scalar(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_scalar_v = __is_scalar(_Tp);
 #endif
 
 #else // __has_keyword(__is_scalar)
 
 template <class _Tp> struct __is_block : false_type {};
 #if defined(_LIBCPP_HAS_EXTENSION_BLOCKS)
 template <class _Rp, class ..._Args> struct __is_block<_Rp (^)(_Args...)> : true_type {};
 #endif
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_scalar
     : public integral_constant<bool, is_arithmetic<_Tp>::value     ||
                                      is_member_pointer<_Tp>::value ||
                                      is_pointer<_Tp>::value        ||
                                      __is_nullptr_t<_Tp>::value    ||
                                      __is_block<_Tp>::value        ||
                                      is_enum<_Tp>::value           > {};
 
 template <> struct _LIBCPP_TEMPLATE_VIS is_scalar<nullptr_t> : public true_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_scalar)
 
 // is_object
 
 #if __has_keyword(__is_object)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_object : _BoolConstant<__is_object(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_object_v = __is_object(_Tp);
 #endif
 
 #else // __has_keyword(__is_object)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_object
     : public integral_constant<bool, is_scalar<_Tp>::value ||
                                      is_array<_Tp>::value  ||
                                      is_union<_Tp>::value  ||
                                      is_class<_Tp>::value  > {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_object_v = is_object<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_object)
 
 // is_compound
 
 // >= 11 because in C++03 nullptr isn't actually nullptr
 #if __has_keyword(__is_compound) && !defined(_LIBCPP_CXX03_LANG)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_compound : _BoolConstant<__is_compound(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_compound_v = __is_compound(_Tp);
 #endif
 
 #else // __has_keyword(__is_compound)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_compound
     : public integral_constant<bool, !is_fundamental<_Tp>::value> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_compound_v = is_compound<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_compound)
 
 // __is_referenceable  [defns.referenceable]
 
 struct __is_referenceable_impl {
     template <class _Tp> static _Tp& __test(int);
     template <class _Tp> static __two __test(...);
 };
 
 template <class _Tp>
 struct __is_referenceable : integral_constant<bool,
     _IsNotSame<decltype(__is_referenceable_impl::__test<_Tp>(0)), __two>::value> {};
 
 
 // add_const
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_const {
   typedef _LIBCPP_NODEBUG const _Tp type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_const_t = typename add_const<_Tp>::type;
 #endif
 
 // add_volatile
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_volatile {
   typedef _LIBCPP_NODEBUG volatile _Tp type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_volatile_t = typename add_volatile<_Tp>::type;
 #endif
 
 // add_cv
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_cv {
   typedef _LIBCPP_NODEBUG const volatile _Tp type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_cv_t = typename add_cv<_Tp>::type;
 #endif
 
 // remove_reference
 
 #if __has_keyword(__remove_reference)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS remove_reference { typedef __remove_reference(_Tp) type; };
 
 #else // __has_keyword(__remove_reference)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference        {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference<_Tp&>  {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference<_Tp&&> {typedef _LIBCPP_NODEBUG _Tp type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_reference_t = typename remove_reference<_Tp>::type;
 #endif
 
 #endif // __has_keyword(__remove_reference)
 
 // add_lvalue_reference
 
 template <class _Tp, bool = __is_referenceable<_Tp>::value> struct __add_lvalue_reference_impl            { typedef _LIBCPP_NODEBUG _Tp  type; };
 template <class _Tp                                       > struct __add_lvalue_reference_impl<_Tp, true> { typedef _LIBCPP_NODEBUG _Tp& type; };
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_lvalue_reference
 {typedef _LIBCPP_NODEBUG typename  __add_lvalue_reference_impl<_Tp>::type type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_lvalue_reference_t = typename add_lvalue_reference<_Tp>::type;
 #endif
 
 template <class _Tp, bool = __is_referenceable<_Tp>::value> struct __add_rvalue_reference_impl            { typedef _LIBCPP_NODEBUG _Tp   type; };
 template <class _Tp                                       > struct __add_rvalue_reference_impl<_Tp, true> { typedef _LIBCPP_NODEBUG _Tp&& type; };
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_rvalue_reference
 {typedef _LIBCPP_NODEBUG typename __add_rvalue_reference_impl<_Tp>::type type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_rvalue_reference_t = typename add_rvalue_reference<_Tp>::type;
 #endif
 
 // Suppress deprecation notice for volatile-qualified return type resulting
 // from volatile-qualified types _Tp.
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <class _Tp> _Tp&& __declval(int);
 template <class _Tp> _Tp   __declval(long);
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 template <class _Tp>
 decltype(__declval<_Tp>(0))
 declval() _NOEXCEPT;
 
 // __uncvref
 
 template <class _Tp>
 struct __uncvref  {
     typedef _LIBCPP_NODEBUG typename remove_cv<typename remove_reference<_Tp>::type>::type type;
 };
 
 template <class _Tp>
 struct __unconstref {
     typedef _LIBCPP_NODEBUG typename remove_const<typename remove_reference<_Tp>::type>::type type;
 };
 
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Tp>
 using __uncvref_t _LIBCPP_NODEBUG = typename __uncvref<_Tp>::type;
 #endif
 
 // __is_same_uncvref
 
 template <class _Tp, class _Up>
 struct __is_same_uncvref : _IsSame<typename __uncvref<_Tp>::type,
                                    typename __uncvref<_Up>::type> {};
 
 #if _LIBCPP_STD_VER > 17
 // remove_cvref - same as __uncvref
 template <class _Tp>
 struct remove_cvref : public __uncvref<_Tp> {};
 
 template <class _Tp> using remove_cvref_t = typename remove_cvref<_Tp>::type;
 #endif
 
 
 struct __any
 {
     __any(...);
 };
 
 // remove_pointer
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer                      {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp*>                {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const>          {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* volatile>       {typedef _LIBCPP_NODEBUG _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const volatile> {typedef _LIBCPP_NODEBUG _Tp type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_pointer_t = typename remove_pointer<_Tp>::type;
 #endif
 
 // add_pointer
 
 template <class _Tp,
         bool = __is_referenceable<_Tp>::value ||
                 _IsSame<typename remove_cv<_Tp>::type, void>::value>
 struct __add_pointer_impl
     {typedef _LIBCPP_NODEBUG typename remove_reference<_Tp>::type* type;};
 template <class _Tp> struct __add_pointer_impl<_Tp, false>
     {typedef _LIBCPP_NODEBUG _Tp type;};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_pointer
     {typedef _LIBCPP_NODEBUG typename __add_pointer_impl<_Tp>::type type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using add_pointer_t = typename add_pointer<_Tp>::type;
 #endif
 
 // type_identity
 #if _LIBCPP_STD_VER > 17
 template<class _Tp> struct type_identity { typedef _Tp type; };
 template<class _Tp> using type_identity_t = typename type_identity<_Tp>::type;
 #endif
 
 // is_signed
 
 #if __has_keyword(__is_signed)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_signed : _BoolConstant<__is_signed(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_signed_v = __is_signed(_Tp);
 #endif
 
 #else // __has_keyword(__is_signed)
 
 template <class _Tp, bool = is_integral<_Tp>::value>
 struct __libcpp_is_signed_impl : public _LIBCPP_BOOL_CONSTANT(_Tp(-1) < _Tp(0)) {};
 
 template <class _Tp>
 struct __libcpp_is_signed_impl<_Tp, false> : public true_type {};  // floating point
 
 template <class _Tp, bool = is_arithmetic<_Tp>::value>
 struct __libcpp_is_signed : public __libcpp_is_signed_impl<_Tp> {};
 
 template <class _Tp> struct __libcpp_is_signed<_Tp, false> : public false_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_signed : public __libcpp_is_signed<_Tp> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_signed_v = is_signed<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_signed)
 
 // is_unsigned
 
 // Before Clang 13, __is_unsigned returned true for enums with signed underlying type.
 // No currently-released version of AppleClang contains the fixed intrinsic.
 #if __has_keyword(__is_unsigned) &&                                            \
     !(defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER < 1300) &&               \
     !defined(_LIBCPP_APPLE_CLANG_VER)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_unsigned : _BoolConstant<__is_unsigned(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_unsigned_v = __is_unsigned(_Tp);
 #endif
 
 #else // __has_keyword(__is_unsigned)
 
 template <class _Tp, bool = is_integral<_Tp>::value>
 struct __libcpp_is_unsigned_impl : public _LIBCPP_BOOL_CONSTANT(_Tp(0) < _Tp(-1)) {};
 
 template <class _Tp>
 struct __libcpp_is_unsigned_impl<_Tp, false> : public false_type {};  // floating point
 
 template <class _Tp, bool = is_arithmetic<_Tp>::value>
 struct __libcpp_is_unsigned : public __libcpp_is_unsigned_impl<_Tp> {};
 
 template <class _Tp> struct __libcpp_is_unsigned<_Tp, false> : public false_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_unsigned : public __libcpp_is_unsigned<_Tp> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_unsigned_v = is_unsigned<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_unsigned)
 
 // rank
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS rank
     : public integral_constant<size_t, 0> {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS rank<_Tp[]>
     : public integral_constant<size_t, rank<_Tp>::value + 1> {};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS rank<_Tp[_Np]>
     : public integral_constant<size_t, rank<_Tp>::value + 1> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr size_t rank_v = rank<_Tp>::value;
 #endif
 
 // extent
 
 #if __has_keyword(__array_extent)
 
 template<class _Tp, size_t _Dim = 0>
 struct _LIBCPP_TEMPLATE_VIS extent
     : integral_constant<size_t, __array_extent(_Tp, _Dim)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, unsigned _Ip = 0>
 inline constexpr size_t extent_v = __array_extent(_Tp, _Ip);
 #endif
 
 #else // __has_keyword(__array_extent)
 
 template <class _Tp, unsigned _Ip = 0> struct _LIBCPP_TEMPLATE_VIS extent
     : public integral_constant<size_t, 0> {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[], 0>
     : public integral_constant<size_t, 0> {};
 template <class _Tp, unsigned _Ip> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[], _Ip>
     : public integral_constant<size_t, extent<_Tp, _Ip-1>::value> {};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[_Np], 0>
     : public integral_constant<size_t, _Np> {};
 template <class _Tp, size_t _Np, unsigned _Ip> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[_Np], _Ip>
     : public integral_constant<size_t, extent<_Tp, _Ip-1>::value> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, unsigned _Ip = 0>
 inline constexpr size_t extent_v = extent<_Tp, _Ip>::value;
 #endif
 
 #endif // __has_keyword(__array_extent)
 
 // remove_extent
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_extent
     {typedef _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_extent<_Tp[]>
     {typedef _Tp type;};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS remove_extent<_Tp[_Np]>
     {typedef _Tp type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_extent_t = typename remove_extent<_Tp>::type;
 #endif
 
 // remove_all_extents
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_all_extents
     {typedef _Tp type;};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_all_extents<_Tp[]>
     {typedef typename remove_all_extents<_Tp>::type type;};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS remove_all_extents<_Tp[_Np]>
     {typedef typename remove_all_extents<_Tp>::type type;};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using remove_all_extents_t = typename remove_all_extents<_Tp>::type;
 #endif
 
 #if _LIBCPP_STD_VER > 17
 // is_bounded_array
 
 template <class>                 struct _LIBCPP_TEMPLATE_VIS is_bounded_array           : false_type {};
 template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS is_bounded_array<_Tp[_Np]> : true_type {};
 
 template <class _Tp>
 inline constexpr
 bool is_bounded_array_v  = is_bounded_array<_Tp>::value;
 
 // is_unbounded_array
 
 template <class>     struct _LIBCPP_TEMPLATE_VIS is_unbounded_array        : false_type {};
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_unbounded_array<_Tp[]> : true_type {};
 
 template <class _Tp>
 inline constexpr
 bool is_unbounded_array_v  = is_unbounded_array<_Tp>::value;
 #endif
 
 // decay
 
 template <class _Up, bool>
 struct __decay {
     typedef _LIBCPP_NODEBUG typename remove_cv<_Up>::type type;
 };
 
 template <class _Up>
 struct __decay<_Up, true> {
 public:
     typedef _LIBCPP_NODEBUG typename conditional
                      <
                          is_array<_Up>::value,
-                         typename remove_extent<_Up>::type*,
+                         typename add_pointer<typename remove_extent<_Up>::type>::type,
                          typename conditional
                          <
                               is_function<_Up>::value,
                               typename add_pointer<_Up>::type,
                               typename remove_cv<_Up>::type
                          >::type
                      >::type type;
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS decay
 {
 private:
     typedef _LIBCPP_NODEBUG typename remove_reference<_Tp>::type _Up;
 public:
     typedef _LIBCPP_NODEBUG typename __decay<_Up, __is_referenceable<_Up>::value>::type type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using decay_t = typename decay<_Tp>::type;
 #endif
 
 // is_abstract
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_abstract
     : public integral_constant<bool, __is_abstract(_Tp)> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_abstract_v = is_abstract<_Tp>::value;
 #endif
 
 // is_final
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
 __libcpp_is_final : public integral_constant<bool, __is_final(_Tp)> {};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
 is_final : public integral_constant<bool, __is_final(_Tp)> {};
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_final_v = is_final<_Tp>::value;
 #endif
 
 // is_aggregate
 #if _LIBCPP_STD_VER > 14
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
 is_aggregate : public integral_constant<bool, __is_aggregate(_Tp)> {};
 
 template <class _Tp>
 inline constexpr bool is_aggregate_v = is_aggregate<_Tp>::value;
 
 #endif // _LIBCPP_STD_VER > 14
 
 // is_base_of
 
 template <class _Bp, class _Dp>
 struct _LIBCPP_TEMPLATE_VIS is_base_of
     : public integral_constant<bool, __is_base_of(_Bp, _Dp)> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Bp, class _Dp>
 inline constexpr bool is_base_of_v = is_base_of<_Bp, _Dp>::value;
 #endif
 
 // __is_core_convertible
 
 // [conv.general]/3 says "E is convertible to T" whenever "T t=E;" is well-formed.
 // We can't test for that, but we can test implicit convertibility by passing it
 // to a function. Notice that __is_core_convertible<void,void> is false,
 // and __is_core_convertible<immovable-type,immovable-type> is true in C++17 and later.
 
 template <class _Tp, class _Up, class = void>
 struct __is_core_convertible : public false_type {};
 
 template <class _Tp, class _Up>
 struct __is_core_convertible<_Tp, _Up, decltype(
     static_cast<void(*)(_Up)>(0) ( static_cast<_Tp(*)()>(0)() )
 )> : public true_type {};
 
 // is_convertible
 
 #if __has_feature(is_convertible_to) && !defined(_LIBCPP_USE_IS_CONVERTIBLE_FALLBACK)
 
 template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS is_convertible
     : public integral_constant<bool, __is_convertible_to(_T1, _T2)> {};
 
 #else  // __has_feature(is_convertible_to)
 
 namespace __is_convertible_imp
 {
 template <class _Tp> void  __test_convert(_Tp);
 
 template <class _From, class _To, class = void>
 struct __is_convertible_test : public false_type {};
 
 template <class _From, class _To>
 struct __is_convertible_test<_From, _To,
     decltype(__is_convertible_imp::__test_convert<_To>(declval<_From>()))> : public true_type
 {};
 
 template <class _Tp, bool _IsArray =    is_array<_Tp>::value,
                      bool _IsFunction = is_function<_Tp>::value,
                      bool _IsVoid =     is_void<_Tp>::value>
                      struct __is_array_function_or_void                          {enum {value = 0};};
 template <class _Tp> struct __is_array_function_or_void<_Tp, true, false, false> {enum {value = 1};};
 template <class _Tp> struct __is_array_function_or_void<_Tp, false, true, false> {enum {value = 2};};
 template <class _Tp> struct __is_array_function_or_void<_Tp, false, false, true> {enum {value = 3};};
 }
 
 template <class _Tp,
     unsigned = __is_convertible_imp::__is_array_function_or_void<typename remove_reference<_Tp>::type>::value>
 struct __is_convertible_check
 {
     static const size_t __v = 0;
 };
 
 template <class _Tp>
 struct __is_convertible_check<_Tp, 0>
 {
     static const size_t __v = sizeof(_Tp);
 };
 
 template <class _T1, class _T2,
     unsigned _T1_is_array_function_or_void = __is_convertible_imp::__is_array_function_or_void<_T1>::value,
     unsigned _T2_is_array_function_or_void = __is_convertible_imp::__is_array_function_or_void<_T2>::value>
 struct __is_convertible
     : public integral_constant<bool,
         __is_convertible_imp::__is_convertible_test<_T1, _T2>::value
     >
 {};
 
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 1> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 1> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 1> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 1> : public false_type {};
 
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 2> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 2> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 2> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 2> : public false_type {};
 
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 3> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 3> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 3> : public false_type {};
 template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 3> : public true_type {};
 
 template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS is_convertible
     : public __is_convertible<_T1, _T2>
 {
     static const size_t __complete_check1 = __is_convertible_check<_T1>::__v;
     static const size_t __complete_check2 = __is_convertible_check<_T2>::__v;
 };
 
 #endif // __has_feature(is_convertible_to)
 
 #if _LIBCPP_STD_VER > 14
 template <class _From, class _To>
 inline constexpr bool is_convertible_v = is_convertible<_From, _To>::value;
 #endif
 
 // is_nothrow_convertible
 
 #if _LIBCPP_STD_VER > 17
 
 template <typename _Tp>
 static void __test_noexcept(_Tp) noexcept;
 
 template<typename _Fm, typename _To>
 static bool_constant<noexcept(_VSTD::__test_noexcept<_To>(declval<_Fm>()))>
 __is_nothrow_convertible_test();
 
 template <typename _Fm, typename _To>
 struct __is_nothrow_convertible_helper: decltype(__is_nothrow_convertible_test<_Fm, _To>())
 { };
 
 template <typename _Fm, typename _To>
 struct is_nothrow_convertible : _Or<
     _And<is_void<_To>, is_void<_Fm>>,
     _Lazy<_And, is_convertible<_Fm, _To>, __is_nothrow_convertible_helper<_Fm, _To>>
 >::type { };
 
 template <typename _Fm, typename _To>
 inline constexpr bool is_nothrow_convertible_v = is_nothrow_convertible<_Fm, _To>::value;
 
 #endif // _LIBCPP_STD_VER > 17
 
 // is_empty
 
 #if __has_feature(is_empty) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_empty
     : public integral_constant<bool, __is_empty(_Tp)> {};
 
 #else  // __has_feature(is_empty)
 
 template <class _Tp>
 struct __is_empty1
     : public _Tp
 {
     double __lx;
 };
 
 struct __is_empty2
 {
     double __lx;
 };
 
 template <class _Tp, bool = is_class<_Tp>::value>
 struct __libcpp_empty : public integral_constant<bool, sizeof(__is_empty1<_Tp>) == sizeof(__is_empty2)> {};
 
 template <class _Tp> struct __libcpp_empty<_Tp, false> : public false_type {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_empty : public __libcpp_empty<_Tp> {};
 
 #endif // __has_feature(is_empty)
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_empty_v = is_empty<_Tp>::value;
 #endif
 
 // is_polymorphic
 
 #if __has_feature(is_polymorphic) || defined(_LIBCPP_COMPILER_MSVC)
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_polymorphic
     : public integral_constant<bool, __is_polymorphic(_Tp)> {};
 
 #else
 
 template<typename _Tp> char &__is_polymorphic_impl(
     typename enable_if<sizeof((_Tp*)dynamic_cast<const volatile void*>(declval<_Tp*>())) != 0,
                        int>::type);
 template<typename _Tp> __two &__is_polymorphic_impl(...);
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_polymorphic
     : public integral_constant<bool, sizeof(__is_polymorphic_impl<_Tp>(0)) == 1> {};
 
 #endif // __has_feature(is_polymorphic)
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_polymorphic_v = is_polymorphic<_Tp>::value;
 #endif
 
 // has_virtual_destructor
 
 #if __has_feature(has_virtual_destructor) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_virtual_destructor
     : public integral_constant<bool, __has_virtual_destructor(_Tp)> {};
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_virtual_destructor
     : public false_type {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool has_virtual_destructor_v = has_virtual_destructor<_Tp>::value;
 #endif
 
 // has_unique_object_representations
 
 #if _LIBCPP_STD_VER > 14
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_unique_object_representations
     : public integral_constant<bool,
        __has_unique_object_representations(remove_cv_t<remove_all_extents_t<_Tp>>)> {};
 
 template <class _Tp>
 inline constexpr bool has_unique_object_representations_v = has_unique_object_representations<_Tp>::value;
 
 #endif
 
 // alignment_of
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS alignment_of
     : public integral_constant<size_t, _LIBCPP_ALIGNOF(_Tp)> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr size_t alignment_of_v = alignment_of<_Tp>::value;
 #endif
 
 // aligned_storage
 
 template <class _Hp, class _Tp>
 struct __type_list
 {
     typedef _Hp _Head;
     typedef _Tp _Tail;
 };
 
 struct __nat
 {
 #ifndef _LIBCPP_CXX03_LANG
     __nat() = delete;
     __nat(const __nat&) = delete;
     __nat& operator=(const __nat&) = delete;
     ~__nat() = delete;
 #endif
 };
 
 template <class _Tp>
 struct __align_type
 {
     static const size_t value = _LIBCPP_PREFERRED_ALIGNOF(_Tp);
     typedef _Tp type;
 };
 
 struct __struct_double {long double __lx;};
 struct __struct_double4 {double __lx[4];};
 
 typedef
     __type_list<__align_type<unsigned char>,
     __type_list<__align_type<unsigned short>,
     __type_list<__align_type<unsigned int>,
     __type_list<__align_type<unsigned long>,
     __type_list<__align_type<unsigned long long>,
     __type_list<__align_type<double>,
     __type_list<__align_type<long double>,
     __type_list<__align_type<__struct_double>,
     __type_list<__align_type<__struct_double4>,
     __type_list<__align_type<int*>,
     __nat
     > > > > > > > > > > __all_types;
 
 template <size_t _Align>
 struct _ALIGNAS(_Align) __fallback_overaligned {};
 
 template <class _TL, size_t _Align> struct __find_pod;
 
 template <class _Hp, size_t _Align>
 struct __find_pod<__type_list<_Hp, __nat>, _Align>
 {
     typedef typename conditional<
                              _Align == _Hp::value,
                              typename _Hp::type,
                              __fallback_overaligned<_Align>
                          >::type type;
 };
 
 template <class _Hp, class _Tp, size_t _Align>
 struct __find_pod<__type_list<_Hp, _Tp>, _Align>
 {
     typedef typename conditional<
                              _Align == _Hp::value,
                              typename _Hp::type,
                              typename __find_pod<_Tp, _Align>::type
                          >::type type;
 };
 
 template <class _TL, size_t _Len> struct __find_max_align;
 
 template <class _Hp, size_t _Len>
 struct __find_max_align<__type_list<_Hp, __nat>, _Len> : public integral_constant<size_t, _Hp::value> {};
 
 template <size_t _Len, size_t _A1, size_t _A2>
 struct __select_align
 {
 private:
     static const size_t __min = _A2 < _A1 ? _A2 : _A1;
     static const size_t __max = _A1 < _A2 ? _A2 : _A1;
 public:
     static const size_t value = _Len < __max ? __min : __max;
 };
 
 template <class _Hp, class _Tp, size_t _Len>
 struct __find_max_align<__type_list<_Hp, _Tp>, _Len>
     : public integral_constant<size_t, __select_align<_Len, _Hp::value, __find_max_align<_Tp, _Len>::value>::value> {};
 
 template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
 struct _LIBCPP_TEMPLATE_VIS aligned_storage
 {
     typedef typename __find_pod<__all_types, _Align>::type _Aligner;
     union type
     {
         _Aligner __align;
         unsigned char __data[(_Len + _Align - 1)/_Align * _Align];
     };
 };
 
 #if _LIBCPP_STD_VER > 11
 template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
     using aligned_storage_t = typename aligned_storage<_Len, _Align>::type;
 #endif
 
 #define _CREATE_ALIGNED_STORAGE_SPECIALIZATION(n) \
 template <size_t _Len>\
 struct _LIBCPP_TEMPLATE_VIS aligned_storage<_Len, n>\
 {\
     struct _ALIGNAS(n) type\
     {\
         unsigned char __lx[(_Len + n - 1)/n * n];\
     };\
 }
 
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x1);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x2);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x4);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x8);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x10);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x20);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x40);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x80);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x100);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x200);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x400);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x800);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x1000);
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x2000);
 // PE/COFF does not support alignment beyond 8192 (=0x2000)
 #if !defined(_LIBCPP_OBJECT_FORMAT_COFF)
 _CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x4000);
 #endif // !defined(_LIBCPP_OBJECT_FORMAT_COFF)
 
 #undef _CREATE_ALIGNED_STORAGE_SPECIALIZATION
 
 
 // aligned_union
 
 template <size_t _I0, size_t ..._In>
 struct __static_max;
 
 template <size_t _I0>
 struct __static_max<_I0>
 {
     static const size_t value = _I0;
 };
 
 template <size_t _I0, size_t _I1, size_t ..._In>
 struct __static_max<_I0, _I1, _In...>
 {
     static const size_t value = _I0 >= _I1 ? __static_max<_I0, _In...>::value :
                                              __static_max<_I1, _In...>::value;
 };
 
 template <size_t _Len, class _Type0, class ..._Types>
 struct aligned_union
 {
     static const size_t alignment_value = __static_max<_LIBCPP_PREFERRED_ALIGNOF(_Type0),
                                                        _LIBCPP_PREFERRED_ALIGNOF(_Types)...>::value;
     static const size_t __len = __static_max<_Len, sizeof(_Type0),
                                              sizeof(_Types)...>::value;
     typedef typename aligned_storage<__len, alignment_value>::type type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <size_t _Len, class ..._Types> using aligned_union_t = typename aligned_union<_Len, _Types...>::type;
 #endif
 
 template <class _Tp>
 struct __numeric_type
 {
    static void __test(...);
    static float __test(float);
    static double __test(char);
    static double __test(int);
    static double __test(unsigned);
    static double __test(long);
    static double __test(unsigned long);
    static double __test(long long);
    static double __test(unsigned long long);
    static double __test(double);
    static long double __test(long double);
 
    typedef decltype(__test(declval<_Tp>())) type;
    static const bool value = _IsNotSame<type, void>::value;
 };
 
 template <>
 struct __numeric_type<void>
 {
    static const bool value = true;
 };
 
 // __promote
 
 template <class _A1, class _A2 = void, class _A3 = void,
           bool = __numeric_type<_A1>::value &&
                  __numeric_type<_A2>::value &&
                  __numeric_type<_A3>::value>
 class __promote_imp
 {
 public:
     static const bool value = false;
 };
 
 template <class _A1, class _A2, class _A3>
 class __promote_imp<_A1, _A2, _A3, true>
 {
 private:
     typedef typename __promote_imp<_A1>::type __type1;
     typedef typename __promote_imp<_A2>::type __type2;
     typedef typename __promote_imp<_A3>::type __type3;
 public:
     typedef decltype(__type1() + __type2() + __type3()) type;
     static const bool value = true;
 };
 
 template <class _A1, class _A2>
 class __promote_imp<_A1, _A2, void, true>
 {
 private:
     typedef typename __promote_imp<_A1>::type __type1;
     typedef typename __promote_imp<_A2>::type __type2;
 public:
     typedef decltype(__type1() + __type2()) type;
     static const bool value = true;
 };
 
 template <class _A1>
 class __promote_imp<_A1, void, void, true>
 {
 public:
     typedef typename __numeric_type<_A1>::type type;
     static const bool value = true;
 };
 
 template <class _A1, class _A2 = void, class _A3 = void>
 class __promote : public __promote_imp<_A1, _A2, _A3> {};
 
 // make_signed / make_unsigned
 
 typedef
     __type_list<signed char,
     __type_list<signed short,
     __type_list<signed int,
     __type_list<signed long,
     __type_list<signed long long,
 #ifndef _LIBCPP_HAS_NO_INT128
     __type_list<__int128_t,
 #endif
     __nat
 #ifndef _LIBCPP_HAS_NO_INT128
     >
 #endif
     > > > > > __signed_types;
 
 typedef
     __type_list<unsigned char,
     __type_list<unsigned short,
     __type_list<unsigned int,
     __type_list<unsigned long,
     __type_list<unsigned long long,
 #ifndef _LIBCPP_HAS_NO_INT128
     __type_list<__uint128_t,
 #endif
     __nat
 #ifndef _LIBCPP_HAS_NO_INT128
     >
 #endif
     > > > > > __unsigned_types;
 
 template <class _TypeList, size_t _Size, bool = _Size <= sizeof(typename _TypeList::_Head)> struct __find_first;
 
 template <class _Hp, class _Tp, size_t _Size>
 struct __find_first<__type_list<_Hp, _Tp>, _Size, true>
 {
     typedef _LIBCPP_NODEBUG _Hp type;
 };
 
 template <class _Hp, class _Tp, size_t _Size>
 struct __find_first<__type_list<_Hp, _Tp>, _Size, false>
 {
     typedef _LIBCPP_NODEBUG typename __find_first<_Tp, _Size>::type type;
 };
 
 template <class _Tp, class _Up, bool = is_const<typename remove_reference<_Tp>::type>::value,
                              bool = is_volatile<typename remove_reference<_Tp>::type>::value>
 struct __apply_cv
 {
     typedef _LIBCPP_NODEBUG _Up type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp, _Up, true, false>
 {
     typedef _LIBCPP_NODEBUG const _Up type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp, _Up, false, true>
 {
     typedef volatile _Up type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp, _Up, true, true>
 {
     typedef const volatile _Up type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp&, _Up, false, false>
 {
     typedef _Up& type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp&, _Up, true, false>
 {
     typedef const _Up& type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp&, _Up, false, true>
 {
     typedef volatile _Up& type;
 };
 
 template <class _Tp, class _Up>
 struct __apply_cv<_Tp&, _Up, true, true>
 {
     typedef const volatile _Up& type;
 };
 
 template <class _Tp, bool = is_integral<_Tp>::value || is_enum<_Tp>::value>
 struct __make_signed {};
 
 template <class _Tp>
 struct __make_signed<_Tp, true>
 {
     typedef typename __find_first<__signed_types, sizeof(_Tp)>::type type;
 };
 
 template <> struct __make_signed<bool,               true> {};
 template <> struct __make_signed<  signed short,     true> {typedef short     type;};
 template <> struct __make_signed<unsigned short,     true> {typedef short     type;};
 template <> struct __make_signed<  signed int,       true> {typedef int       type;};
 template <> struct __make_signed<unsigned int,       true> {typedef int       type;};
 template <> struct __make_signed<  signed long,      true> {typedef long      type;};
 template <> struct __make_signed<unsigned long,      true> {typedef long      type;};
 template <> struct __make_signed<  signed long long, true> {typedef long long type;};
 template <> struct __make_signed<unsigned long long, true> {typedef long long type;};
 #ifndef _LIBCPP_HAS_NO_INT128
 template <> struct __make_signed<__int128_t,         true> {typedef __int128_t type;};
 template <> struct __make_signed<__uint128_t,        true> {typedef __int128_t type;};
 #endif
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS make_signed
 {
     typedef typename __apply_cv<_Tp, typename __make_signed<typename remove_cv<_Tp>::type>::type>::type type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using make_signed_t = typename make_signed<_Tp>::type;
 #endif
 
 template <class _Tp, bool = is_integral<_Tp>::value || is_enum<_Tp>::value>
 struct __make_unsigned {};
 
 template <class _Tp>
 struct __make_unsigned<_Tp, true>
 {
     typedef typename __find_first<__unsigned_types, sizeof(_Tp)>::type type;
 };
 
 template <> struct __make_unsigned<bool,               true> {};
 template <> struct __make_unsigned<  signed short,     true> {typedef unsigned short     type;};
 template <> struct __make_unsigned<unsigned short,     true> {typedef unsigned short     type;};
 template <> struct __make_unsigned<  signed int,       true> {typedef unsigned int       type;};
 template <> struct __make_unsigned<unsigned int,       true> {typedef unsigned int       type;};
 template <> struct __make_unsigned<  signed long,      true> {typedef unsigned long      type;};
 template <> struct __make_unsigned<unsigned long,      true> {typedef unsigned long      type;};
 template <> struct __make_unsigned<  signed long long, true> {typedef unsigned long long type;};
 template <> struct __make_unsigned<unsigned long long, true> {typedef unsigned long long type;};
 #ifndef _LIBCPP_HAS_NO_INT128
 template <> struct __make_unsigned<__int128_t,         true> {typedef __uint128_t        type;};
 template <> struct __make_unsigned<__uint128_t,        true> {typedef __uint128_t        type;};
 #endif
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS make_unsigned
 {
     typedef typename __apply_cv<_Tp, typename __make_unsigned<typename remove_cv<_Tp>::type>::type>::type type;
 };
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using make_unsigned_t = typename make_unsigned<_Tp>::type;
 #endif
 
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr
 typename make_unsigned<_Tp>::type __to_unsigned_like(_Tp __x) noexcept {
     return static_cast<typename make_unsigned<_Tp>::type>(__x);
 }
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class...> using void_t = void;
 #endif
 
 #if _LIBCPP_STD_VER > 17
 // Let COND_RES(X, Y) be:
 template <class _Tp, class _Up>
 using __cond_type = decltype(false ? declval<_Tp>() : declval<_Up>());
 
 template <class _Tp, class _Up, class = void>
 struct __common_type3 {};
 
 // sub-bullet 4 - "if COND_RES(CREF(D1), CREF(D2)) denotes a type..."
 template <class _Tp, class _Up>
 struct __common_type3<_Tp, _Up, void_t<__cond_type<const _Tp&, const _Up&>>>
 {
     using type = remove_cvref_t<__cond_type<const _Tp&, const _Up&>>;
 };
 
 template <class _Tp, class _Up, class = void>
 struct __common_type2_imp : __common_type3<_Tp, _Up> {};
 #else
 template <class _Tp, class _Up, class = void>
 struct __common_type2_imp {};
 #endif
 
 // sub-bullet 3 - "if decay_t<decltype(false ? declval<D1>() : declval<D2>())> ..."
 template <class _Tp, class _Up>
 struct __common_type2_imp<_Tp, _Up,
                           typename __void_t<decltype(
                                             true ? declval<_Tp>() : declval<_Up>()
                                             )>::type>
 {
   typedef _LIBCPP_NODEBUG typename decay<decltype(
                          true ? declval<_Tp>() : declval<_Up>()
                          )>::type type;
 };
 
 template <class, class = void>
 struct __common_type_impl {};
 
 // Clang provides variadic templates in C++03 as an extension.
 #if !defined(_LIBCPP_CXX03_LANG) || defined(__clang__)
 # define _LIBCPP_OPTIONAL_PACK(...) , __VA_ARGS__
 template <class... _Tp>
 struct __common_types;
 template <class... _Tp>
 struct _LIBCPP_TEMPLATE_VIS common_type;
 #else
 # define _LIBCPP_OPTIONAL_PACK(...)
 struct __no_arg;
 template <class _Tp, class _Up, class = __no_arg>
 struct __common_types;
 template <class _Tp = __no_arg, class _Up = __no_arg, class _Vp = __no_arg,
           class _Unused = __no_arg>
 struct common_type {
   static_assert(sizeof(_Unused) == 0,
                 "common_type accepts at most 3 arguments in C++03");
 };
 #endif // _LIBCPP_CXX03_LANG
 
 template <class _Tp, class _Up>
 struct __common_type_impl<
     __common_types<_Tp, _Up>,
     typename __void_t<typename common_type<_Tp, _Up>::type>::type>
 {
   typedef typename common_type<_Tp, _Up>::type type;
 };
 
 template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)>
 struct __common_type_impl<
     __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)>,
     typename __void_t<typename common_type<_Tp, _Up>::type>::type>
     : __common_type_impl<__common_types<typename common_type<_Tp, _Up>::type,
                                         _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > {
 };
 
 // bullet 1 - sizeof...(Tp) == 0
 
 template <>
 struct _LIBCPP_TEMPLATE_VIS common_type<> {};
 
 // bullet 2 - sizeof...(Tp) == 1
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS common_type<_Tp>
     : public common_type<_Tp, _Tp> {};
 
 // bullet 3 - sizeof...(Tp) == 2
 
 // sub-bullet 1 - "If is_same_v<T1, D1> is false or ..."
 template <class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS common_type<_Tp, _Up>
     : conditional<
         _IsSame<_Tp, typename decay<_Tp>::type>::value && _IsSame<_Up, typename decay<_Up>::type>::value,
         __common_type2_imp<_Tp, _Up>,
         common_type<typename decay<_Tp>::type, typename decay<_Up>::type>
     >::type
 {};
 
 // bullet 4 - sizeof...(Tp) > 2
 
 template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)>
 struct _LIBCPP_TEMPLATE_VIS
     common_type<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)>
     : __common_type_impl<
           __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > {};
 
 #undef _LIBCPP_OPTIONAL_PACK
 
 #if _LIBCPP_STD_VER > 11
 template <class ..._Tp> using common_type_t = typename common_type<_Tp...>::type;
 #endif
 
 #if _LIBCPP_STD_VER > 11
 // Let COPYCV(FROM, TO) be an alias for type TO with the addition of FROM's
 // top-level cv-qualifiers.
 template <class _From, class _To>
 struct __copy_cv
 {
     using type = _To;
 };
 
 template <class _From, class _To>
 struct __copy_cv<const _From, _To>
 {
     using type = add_const_t<_To>;
 };
 
 template <class _From, class _To>
 struct __copy_cv<volatile _From, _To>
 {
     using type = add_volatile_t<_To>;
 };
 
 template <class _From, class _To>
 struct __copy_cv<const volatile _From, _To>
 {
     using type = add_cv_t<_To>;
 };
 
 template <class _From, class _To>
 using __copy_cv_t = typename __copy_cv<_From, _To>::type;
 
 template <class _From, class _To>
 struct __copy_cvref
 {
     using type = __copy_cv_t<_From, _To>;
 };
 
 template <class _From, class _To>
 struct __copy_cvref<_From&, _To>
 {
     using type = add_lvalue_reference_t<__copy_cv_t<_From, _To>>;
 };
 
 template <class _From, class _To>
 struct __copy_cvref<_From&&, _To>
 {
     using type = add_rvalue_reference_t<__copy_cv_t<_From, _To>>;
 };
 
 template <class _From, class _To>
 using __copy_cvref_t = typename __copy_cvref<_From, _To>::type;
 
 #endif // _LIBCPP_STD_VER > 11
 
 // common_reference
 #if !defined(_LIBCPP_HAS_NO_CONCEPTS)
 // Let COND_RES(X, Y) be:
 template <class _Xp, class _Yp>
 using __cond_res =
     decltype(false ? declval<_Xp(&)()>()() : declval<_Yp(&)()>()());
 
 // Let `XREF(A)` denote a unary alias template `T` such that `T<U>` denotes the same type as `U`
 // with the addition of `A`'s cv and reference qualifiers, for a non-reference cv-unqualified type
 // `U`.
 // [Note: `XREF(A)` is `__xref<A>::template __apply`]
 template <class _Tp>
 struct __xref {
   template<class _Up>
   using __apply = __copy_cvref_t<_Tp, _Up>;
 };
 
 // Given types A and B, let X be remove_reference_t<A>, let Y be remove_reference_t<B>,
 // and let COMMON-REF(A, B) be:
 template<class _Ap, class _Bp, class _Xp = remove_reference_t<_Ap>, class _Yp = remove_reference_t<_Bp>>
 struct __common_ref;
 
 template<class _Xp, class _Yp>
 using __common_ref_t = typename __common_ref<_Xp, _Yp>::__type;
 
 template<class _Xp, class _Yp>
 using __cv_cond_res = __cond_res<__copy_cv_t<_Xp, _Yp>&, __copy_cv_t<_Yp, _Xp>&>;
 
 
 //    If A and B are both lvalue reference types, COMMON-REF(A, B) is
 //    COND-RES(COPYCV(X, Y)&, COPYCV(Y, X)&) if that type exists and is a reference type.
 template<class _Ap, class _Bp, class _Xp, class _Yp>
 requires requires { typename __cv_cond_res<_Xp, _Yp>; } && is_reference_v<__cv_cond_res<_Xp, _Yp>>
 struct __common_ref<_Ap&, _Bp&, _Xp, _Yp>
 {
     using __type = __cv_cond_res<_Xp, _Yp>;
 };
 
 //    Otherwise, let C be remove_reference_t<COMMON-REF(X&, Y&)>&&. ...
 template <class _Xp, class _Yp>
 using __common_ref_C = remove_reference_t<__common_ref_t<_Xp&, _Yp&>>&&;
 
 
 //    .... If A and B are both rvalue reference types, C is well-formed, and
 //    is_convertible_v<A, C> && is_convertible_v<B, C> is true, then COMMON-REF(A, B) is C.
 template<class _Ap, class _Bp, class _Xp, class _Yp>
 requires
   requires { typename __common_ref_C<_Xp, _Yp>; } &&
   is_convertible_v<_Ap&&, __common_ref_C<_Xp, _Yp>> &&
   is_convertible_v<_Bp&&, __common_ref_C<_Xp, _Yp>>
 struct __common_ref<_Ap&&, _Bp&&, _Xp, _Yp>
 {
     using __type = __common_ref_C<_Xp, _Yp>;
 };
 
 //    Otherwise, let D be COMMON-REF(const X&, Y&). ...
 template <class _Tp, class _Up>
 using __common_ref_D = __common_ref_t<const _Tp&, _Up&>;
 
 //    ... If A is an rvalue reference and B is an lvalue reference and D is well-formed and
 //    is_convertible_v<A, D> is true, then COMMON-REF(A, B) is D.
 template<class _Ap, class _Bp, class _Xp, class _Yp>
 requires requires { typename __common_ref_D<_Xp, _Yp>; } &&
          is_convertible_v<_Ap&&, __common_ref_D<_Xp, _Yp>>
 struct __common_ref<_Ap&&, _Bp&, _Xp, _Yp>
 {
     using __type = __common_ref_D<_Xp, _Yp>;
 };
 
 //    Otherwise, if A is an lvalue reference and B is an rvalue reference, then
 //    COMMON-REF(A, B) is COMMON-REF(B, A).
 template<class _Ap, class _Bp, class _Xp, class _Yp>
 struct __common_ref<_Ap&, _Bp&&, _Xp, _Yp> : __common_ref<_Bp&&, _Ap&> {};
 
 //    Otherwise, COMMON-REF(A, B) is ill-formed.
 template<class _Ap, class _Bp, class _Xp, class _Yp>
 struct __common_ref {};
 
 // Note C: For the common_reference trait applied to a parameter pack [...]
 
 template <class...>
 struct common_reference;
 
 template <class... _Types>
 using common_reference_t = typename common_reference<_Types...>::type;
 
 // bullet 1 - sizeof...(T) == 0
 template<>
 struct common_reference<> {};
 
 // bullet 2 - sizeof...(T) == 1
 template <class _Tp>
 struct common_reference<_Tp>
 {
     using type = _Tp;
 };
 
 // bullet 3 - sizeof...(T) == 2
 template <class _Tp, class _Up> struct __common_reference_sub_bullet3;
 template <class _Tp, class _Up> struct __common_reference_sub_bullet2 : __common_reference_sub_bullet3<_Tp, _Up> {};
 template <class _Tp, class _Up> struct __common_reference_sub_bullet1 : __common_reference_sub_bullet2<_Tp, _Up> {};
 
 // sub-bullet 1 - If T1 and T2 are reference types and COMMON-REF(T1, T2) is well-formed, then
 // the member typedef `type` denotes that type.
 template <class _Tp, class _Up> struct common_reference<_Tp, _Up> : __common_reference_sub_bullet1<_Tp, _Up> {};
 
 template <class _Tp, class _Up>
 requires is_reference_v<_Tp> && is_reference_v<_Up> && requires { typename __common_ref_t<_Tp, _Up>; }
 struct __common_reference_sub_bullet1<_Tp, _Up>
 {
     using type = __common_ref_t<_Tp, _Up>;
 };
 
 // sub-bullet 2 - Otherwise, if basic_common_reference<remove_cvref_t<T1>, remove_cvref_t<T2>, XREF(T1), XREF(T2)>::type
 // is well-formed, then the member typedef `type` denotes that type.
 template <class, class, template <class> class, template <class> class> struct basic_common_reference {};
 
 template <class _Tp, class _Up>
 using __basic_common_reference_t = typename basic_common_reference<
     remove_cvref_t<_Tp>, remove_cvref_t<_Up>,
     __xref<_Tp>::template __apply, __xref<_Up>::template __apply>::type;
 
 template <class _Tp, class _Up>
 requires requires { typename __basic_common_reference_t<_Tp, _Up>; }
 struct __common_reference_sub_bullet2<_Tp, _Up>
 {
     using type = __basic_common_reference_t<_Tp, _Up>;
 };
 
 // sub-bullet 3 - Otherwise, if COND-RES(T1, T2) is well-formed,
 // then the member typedef `type` denotes that type.
 template <class _Tp, class _Up>
 requires requires { typename __cond_res<_Tp, _Up>; }
 struct __common_reference_sub_bullet3<_Tp, _Up>
 {
     using type = __cond_res<_Tp, _Up>;
 };
 
 
 // sub-bullet 4 & 5 - Otherwise, if common_type_t<T1, T2> is well-formed,
 //                    then the member typedef `type` denotes that type.
 //                  - Otherwise, there shall be no member `type`.
 template <class _Tp, class _Up> struct __common_reference_sub_bullet3 : common_type<_Tp, _Up> {};
 
 // bullet 4 - If there is such a type `C`, the member typedef type shall denote the same type, if
 //            any, as `common_reference_t<C, Rest...>`.
 template <class _Tp, class _Up, class _Vp, class... _Rest>
 requires requires { typename common_reference_t<_Tp, _Up>; }
 struct common_reference<_Tp, _Up, _Vp, _Rest...>
     : common_reference<common_reference_t<_Tp, _Up>, _Vp, _Rest...>
 {};
 
 // bullet 5 - Otherwise, there shall be no member `type`.
 template <class...> struct common_reference {};
 
 #endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
 
 // is_assignable
 
 template<typename, typename _Tp> struct __select_2nd { typedef _LIBCPP_NODEBUG _Tp type; };
 
 #if __has_keyword(__is_assignable)
 
 template<class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class _Arg>
 inline constexpr bool is_assignable_v = __is_assignable(_Tp, _Arg);
 #endif
 
 #else // __has_keyword(__is_assignable)
 
 template <class _Tp, class _Arg>
 typename __select_2nd<decltype((declval<_Tp>() = declval<_Arg>())), true_type>::type
 __is_assignable_test(int);
 
 template <class, class>
 false_type __is_assignable_test(...);
 
 
 template <class _Tp, class _Arg, bool = is_void<_Tp>::value || is_void<_Arg>::value>
 struct __is_assignable_imp
     : public decltype((_VSTD::__is_assignable_test<_Tp, _Arg>(0))) {};
 
 template <class _Tp, class _Arg>
 struct __is_assignable_imp<_Tp, _Arg, true>
     : public false_type
 {
 };
 
 template <class _Tp, class _Arg>
 struct is_assignable
     : public __is_assignable_imp<_Tp, _Arg> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class _Arg>
 inline constexpr bool is_assignable_v = is_assignable<_Tp, _Arg>::value;
 #endif
 
 #endif // __has_keyword(__is_assignable)
 
 // is_copy_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_copy_assignable
     : public is_assignable<typename add_lvalue_reference<_Tp>::type,
                   typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_copy_assignable_v = is_copy_assignable<_Tp>::value;
 #endif
 
 // is_move_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_move_assignable
     : public is_assignable<typename add_lvalue_reference<_Tp>::type,
                            typename add_rvalue_reference<_Tp>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_move_assignable_v = is_move_assignable<_Tp>::value;
 #endif
 
 // is_destructible
 
 #if __has_keyword(__is_destructible)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_destructible : _BoolConstant<__is_destructible(_Tp)> { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_destructible_v = __is_destructible(_Tp);
 #endif
 
 #else // __has_keyword(__is_destructible)
 
 //  if it's a reference, return true
 //  if it's a function, return false
 //  if it's   void,     return false
 //  if it's an array of unknown bound, return false
 //  Otherwise, return "declval<_Up&>().~_Up()" is well-formed
 //    where _Up is remove_all_extents<_Tp>::type
 
 template <class>
 struct __is_destructible_apply { typedef int type; };
 
 template <typename _Tp>
 struct __is_destructor_wellformed {
     template <typename _Tp1>
     static char  __test (
         typename __is_destructible_apply<decltype(declval<_Tp1&>().~_Tp1())>::type
     );
 
     template <typename _Tp1>
     static __two __test (...);
 
     static const bool value = sizeof(__test<_Tp>(12)) == sizeof(char);
 };
 
 template <class _Tp, bool>
 struct __destructible_imp;
 
 template <class _Tp>
 struct __destructible_imp<_Tp, false>
    : public integral_constant<bool,
         __is_destructor_wellformed<typename remove_all_extents<_Tp>::type>::value> {};
 
 template <class _Tp>
 struct __destructible_imp<_Tp, true>
     : public true_type {};
 
 template <class _Tp, bool>
 struct __destructible_false;
 
 template <class _Tp>
 struct __destructible_false<_Tp, false> : public __destructible_imp<_Tp, is_reference<_Tp>::value> {};
 
 template <class _Tp>
 struct __destructible_false<_Tp, true> : public false_type {};
 
 template <class _Tp>
 struct is_destructible
     : public __destructible_false<_Tp, is_function<_Tp>::value> {};
 
 template <class _Tp>
 struct is_destructible<_Tp[]>
     : public false_type {};
 
 template <>
 struct is_destructible<void>
     : public false_type {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_destructible_v = is_destructible<_Tp>::value;
 #endif
 
 #endif // __has_keyword(__is_destructible)
 
 template <class _MP, bool _IsMemberFunctionPtr, bool _IsMemberObjectPtr>
 struct __member_pointer_traits_imp
 {
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...), true, false>
 {
     typedef _Class _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...), true, false>
 {
     typedef _Class _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const, true, false>
 {
     typedef _Class const _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const, true, false>
 {
     typedef _Class const _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile, true, false>
 {
     typedef _Class volatile _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile, true, false>
 {
     typedef _Class volatile _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile, true, false>
 {
     typedef _Class const volatile _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile, true, false>
 {
     typedef _Class const volatile _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 #if __has_feature(cxx_reference_qualified_functions) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) &, true, false>
 {
     typedef _Class& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) &, true, false>
 {
     typedef _Class& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const&, true, false>
 {
     typedef _Class const& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const&, true, false>
 {
     typedef _Class const& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile&, true, false>
 {
     typedef _Class volatile& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile&, true, false>
 {
     typedef _Class volatile& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile&, true, false>
 {
     typedef _Class const volatile& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile&, true, false>
 {
     typedef _Class const volatile& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) &&, true, false>
 {
     typedef _Class&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) &&, true, false>
 {
     typedef _Class&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const&&, true, false>
 {
     typedef _Class const&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const&&, true, false>
 {
     typedef _Class const&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile&&, true, false>
 {
     typedef _Class volatile&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile&&, true, false>
 {
     typedef _Class volatile&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile&&, true, false>
 {
     typedef _Class const volatile&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param...);
 };
 
 template <class _Rp, class _Class, class ..._Param>
 struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile&&, true, false>
 {
     typedef _Class const volatile&& _ClassType;
     typedef _Rp _ReturnType;
     typedef _Rp (_FnType) (_Param..., ...);
 };
 
 #endif // __has_feature(cxx_reference_qualified_functions) || defined(_LIBCPP_COMPILER_GCC)
 
 
 template <class _Rp, class _Class>
 struct __member_pointer_traits_imp<_Rp _Class::*, false, true>
 {
     typedef _Class _ClassType;
     typedef _Rp _ReturnType;
 };
 
 template <class _MP>
 struct __member_pointer_traits
     : public __member_pointer_traits_imp<typename remove_cv<_MP>::type,
                     is_member_function_pointer<_MP>::value,
                     is_member_object_pointer<_MP>::value>
 {
 //     typedef ... _ClassType;
 //     typedef ... _ReturnType;
 //     typedef ... _FnType;
 };
 
 
 template <class _DecayedFp>
 struct __member_pointer_class_type {};
 
 template <class _Ret, class _ClassType>
 struct __member_pointer_class_type<_Ret _ClassType::*> {
   typedef _ClassType type;
 };
 
 // template <class T, class... Args> struct is_constructible;
 
 template <class _Tp, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_constructible
     : public integral_constant<bool, __is_constructible(_Tp, _Args...)>
 { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class ..._Args>
 inline constexpr bool is_constructible_v = is_constructible<_Tp, _Args...>::value;
 #endif
 
 // is_default_constructible
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_default_constructible
     : public is_constructible<_Tp>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_default_constructible_v = is_default_constructible<_Tp>::value;
 #endif
 
 #ifndef _LIBCPP_CXX03_LANG
 // First of all, we can't implement this check in C++03 mode because the {}
 // default initialization syntax isn't valid.
 // Second, we implement the trait in a funny manner with two defaulted template
 // arguments to workaround Clang's PR43454.
 template <class _Tp>
 void __test_implicit_default_constructible(_Tp);
 
 template <class _Tp, class = void, class = typename is_default_constructible<_Tp>::type>
 struct __is_implicitly_default_constructible
     : false_type
 { };
 
 template <class _Tp>
 struct __is_implicitly_default_constructible<_Tp, decltype(__test_implicit_default_constructible<_Tp const&>({})), true_type>
     : true_type
 { };
 
 template <class _Tp>
 struct __is_implicitly_default_constructible<_Tp, decltype(__test_implicit_default_constructible<_Tp const&>({})), false_type>
     : false_type
 { };
 #endif // !C++03
 
 // is_copy_constructible
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_copy_constructible
     : public is_constructible<_Tp,
                   typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_copy_constructible_v = is_copy_constructible<_Tp>::value;
 #endif
 
 // is_move_constructible
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_move_constructible
     : public is_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_move_constructible_v = is_move_constructible<_Tp>::value;
 #endif
 
 // is_trivially_constructible
 
 template <class _Tp, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible
     : integral_constant<bool, __is_trivially_constructible(_Tp, _Args...)>
 {
 };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class... _Args>
 inline constexpr bool is_trivially_constructible_v = is_trivially_constructible<_Tp, _Args...>::value;
 #endif
 
 // is_trivially_default_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_default_constructible
     : public is_trivially_constructible<_Tp>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_default_constructible_v = is_trivially_default_constructible<_Tp>::value;
 #endif
 
 // is_trivially_copy_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copy_constructible
     : public is_trivially_constructible<_Tp, typename add_lvalue_reference<const _Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_copy_constructible_v = is_trivially_copy_constructible<_Tp>::value;
 #endif
 
 // is_trivially_move_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_move_constructible
     : public is_trivially_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_move_constructible_v = is_trivially_move_constructible<_Tp>::value;
 #endif
 
 // is_trivially_assignable
 
 template <class _Tp, class _Arg>
 struct is_trivially_assignable
     : integral_constant<bool, __is_trivially_assignable(_Tp, _Arg)>
 { };
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class _Arg>
 inline constexpr bool is_trivially_assignable_v = is_trivially_assignable<_Tp, _Arg>::value;
 #endif
 
 // is_trivially_copy_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copy_assignable
     : public is_trivially_assignable<typename add_lvalue_reference<_Tp>::type,
                   typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_copy_assignable_v = is_trivially_copy_assignable<_Tp>::value;
 #endif
 
 // is_trivially_move_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_move_assignable
     : public is_trivially_assignable<typename add_lvalue_reference<_Tp>::type,
                                      typename add_rvalue_reference<_Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_move_assignable_v = is_trivially_move_assignable<_Tp>::value;
 #endif
 
 // is_trivially_destructible
 
 #if __has_keyword(__is_trivially_destructible)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
     : public integral_constant<bool, __is_trivially_destructible(_Tp)> {};
 
 #elif __has_feature(has_trivial_destructor) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
     : public integral_constant<bool, is_destructible<_Tp>::value && __has_trivial_destructor(_Tp)> {};
 
 #else
 
 template <class _Tp> struct __libcpp_trivial_destructor
     : public integral_constant<bool, is_scalar<_Tp>::value ||
                                      is_reference<_Tp>::value> {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
     : public __libcpp_trivial_destructor<typename remove_all_extents<_Tp>::type> {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible<_Tp[]>
     : public false_type {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_destructible_v = is_trivially_destructible<_Tp>::value;
 #endif
 
 // is_nothrow_constructible
 
 #if __has_keyword(__is_nothrow_constructible)
 
 template <class _Tp, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible
     : public integral_constant<bool, __is_nothrow_constructible(_Tp, _Args...)> {};
 
 #else
 
 template <bool, bool, class _Tp, class... _Args> struct __libcpp_is_nothrow_constructible;
 
 template <class _Tp, class... _Args>
 struct __libcpp_is_nothrow_constructible</*is constructible*/true, /*is reference*/false, _Tp, _Args...>
     : public integral_constant<bool, noexcept(_Tp(declval<_Args>()...))>
 {
 };
 
 template <class _Tp>
 void __implicit_conversion_to(_Tp) noexcept { }
 
 template <class _Tp, class _Arg>
 struct __libcpp_is_nothrow_constructible</*is constructible*/true, /*is reference*/true, _Tp, _Arg>
     : public integral_constant<bool, noexcept(_VSTD::__implicit_conversion_to<_Tp>(declval<_Arg>()))>
 {
 };
 
 template <class _Tp, bool _IsReference, class... _Args>
 struct __libcpp_is_nothrow_constructible</*is constructible*/false, _IsReference, _Tp, _Args...>
     : public false_type
 {
 };
 
 template <class _Tp, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible
     : __libcpp_is_nothrow_constructible<is_constructible<_Tp, _Args...>::value, is_reference<_Tp>::value, _Tp, _Args...>
 {
 };
 
 template <class _Tp, size_t _Ns>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible<_Tp[_Ns]>
     : __libcpp_is_nothrow_constructible<is_constructible<_Tp>::value, is_reference<_Tp>::value, _Tp>
 {
 };
 
 #endif // _LIBCPP_HAS_NO_NOEXCEPT
 
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class ..._Args>
 inline constexpr bool is_nothrow_constructible_v = is_nothrow_constructible<_Tp, _Args...>::value;
 #endif
 
 // is_nothrow_default_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_default_constructible
     : public is_nothrow_constructible<_Tp>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_default_constructible_v = is_nothrow_default_constructible<_Tp>::value;
 #endif
 
 // is_nothrow_copy_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_copy_constructible
     : public is_nothrow_constructible<_Tp,
                   typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_copy_constructible_v = is_nothrow_copy_constructible<_Tp>::value;
 #endif
 
 // is_nothrow_move_constructible
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_move_constructible
     : public is_nothrow_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_move_constructible_v = is_nothrow_move_constructible<_Tp>::value;
 #endif
 
 // is_nothrow_assignable
 
 #if __has_keyword(__is_nothrow_assignable)
 
 template <class _Tp, class _Arg>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_assignable
     : public integral_constant<bool, __is_nothrow_assignable(_Tp, _Arg)> {};
 
 #else
 
 template <bool, class _Tp, class _Arg> struct __libcpp_is_nothrow_assignable;
 
 template <class _Tp, class _Arg>
 struct __libcpp_is_nothrow_assignable<false, _Tp, _Arg>
     : public false_type
 {
 };
 
 template <class _Tp, class _Arg>
 struct __libcpp_is_nothrow_assignable<true, _Tp, _Arg>
     : public integral_constant<bool, noexcept(declval<_Tp>() = declval<_Arg>()) >
 {
 };
 
 template <class _Tp, class _Arg>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_assignable
     : public __libcpp_is_nothrow_assignable<is_assignable<_Tp, _Arg>::value, _Tp, _Arg>
 {
 };
 
 #endif // _LIBCPP_HAS_NO_NOEXCEPT
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp, class _Arg>
 inline constexpr bool is_nothrow_assignable_v = is_nothrow_assignable<_Tp, _Arg>::value;
 #endif
 
 // is_nothrow_copy_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_copy_assignable
     : public is_nothrow_assignable<typename add_lvalue_reference<_Tp>::type,
                   typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_copy_assignable_v = is_nothrow_copy_assignable<_Tp>::value;
 #endif
 
 // is_nothrow_move_assignable
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_move_assignable
     : public is_nothrow_assignable<typename add_lvalue_reference<_Tp>::type,
                                      typename add_rvalue_reference<_Tp>::type>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_move_assignable_v = is_nothrow_move_assignable<_Tp>::value;
 #endif
 
 // is_nothrow_destructible
 
 #if !defined(_LIBCPP_CXX03_LANG)
 
 template <bool, class _Tp> struct __libcpp_is_nothrow_destructible;
 
 template <class _Tp>
 struct __libcpp_is_nothrow_destructible<false, _Tp>
     : public false_type
 {
 };
 
 template <class _Tp>
 struct __libcpp_is_nothrow_destructible<true, _Tp>
     : public integral_constant<bool, noexcept(declval<_Tp>().~_Tp()) >
 {
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible
     : public __libcpp_is_nothrow_destructible<is_destructible<_Tp>::value, _Tp>
 {
 };
 
 template <class _Tp, size_t _Ns>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp[_Ns]>
     : public is_nothrow_destructible<_Tp>
 {
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp&>
     : public true_type
 {
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp&&>
     : public true_type
 {
 };
 
 #else
 
 template <class _Tp> struct __libcpp_nothrow_destructor
     : public integral_constant<bool, is_scalar<_Tp>::value ||
                                      is_reference<_Tp>::value> {};
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible
     : public __libcpp_nothrow_destructor<typename remove_all_extents<_Tp>::type> {};
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp[]>
     : public false_type {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_nothrow_destructible_v = is_nothrow_destructible<_Tp>::value;
 #endif
 
 // is_pod
 
 #if __has_feature(is_pod) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pod
     : public integral_constant<bool, __is_pod(_Tp)> {};
 
 #else
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pod
     : public integral_constant<bool, is_trivially_default_constructible<_Tp>::value   &&
                                      is_trivially_copy_constructible<_Tp>::value      &&
                                      is_trivially_copy_assignable<_Tp>::value    &&
                                      is_trivially_destructible<_Tp>::value> {};
 
 #endif
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_pod_v = is_pod<_Tp>::value;
 #endif
 
 // is_literal_type;
 
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 is_literal_type
     : public integral_constant<bool, __is_literal_type(_Tp)>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 _LIBCPP_DEPRECATED_IN_CXX17 inline constexpr bool is_literal_type_v = is_literal_type<_Tp>::value;
 #endif // _LIBCPP_STD_VER > 14
 #endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 
 // is_standard_layout;
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_standard_layout
 #if __has_feature(is_standard_layout) || defined(_LIBCPP_COMPILER_GCC)
     : public integral_constant<bool, __is_standard_layout(_Tp)>
 #else
     : integral_constant<bool, is_scalar<typename remove_all_extents<_Tp>::type>::value>
 #endif
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_standard_layout_v = is_standard_layout<_Tp>::value;
 #endif
 
 // is_trivially_copyable;
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copyable
     : public integral_constant<bool, __is_trivially_copyable(_Tp)>
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivially_copyable_v = is_trivially_copyable<_Tp>::value;
 #endif
 
 // is_trivial;
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivial
 #if __has_feature(is_trivial) || defined(_LIBCPP_COMPILER_GCC)
     : public integral_constant<bool, __is_trivial(_Tp)>
 #else
     : integral_constant<bool, is_trivially_copyable<_Tp>::value &&
                                  is_trivially_default_constructible<_Tp>::value>
 #endif
     {};
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
 inline constexpr bool is_trivial_v = is_trivial<_Tp>::value;
 #endif
 
 template <class _Tp> struct __is_reference_wrapper_impl : public false_type {};
 template <class _Tp> struct __is_reference_wrapper_impl<reference_wrapper<_Tp> > : public true_type {};
 template <class _Tp> struct __is_reference_wrapper
     : public __is_reference_wrapper_impl<typename remove_cv<_Tp>::type> {};
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type,
          class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
 using __enable_if_bullet1 = typename enable_if
     <
         is_member_function_pointer<_DecayFp>::value
         && is_base_of<_ClassT, _DecayA0>::value
     >::type;
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type>
 using __enable_if_bullet2 = typename enable_if
     <
         is_member_function_pointer<_DecayFp>::value
         && __is_reference_wrapper<_DecayA0>::value
     >::type;
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type,
          class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
 using __enable_if_bullet3 = typename enable_if
     <
         is_member_function_pointer<_DecayFp>::value
         && !is_base_of<_ClassT, _DecayA0>::value
         && !__is_reference_wrapper<_DecayA0>::value
     >::type;
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type,
          class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
 using __enable_if_bullet4 = typename enable_if
     <
         is_member_object_pointer<_DecayFp>::value
         && is_base_of<_ClassT, _DecayA0>::value
     >::type;
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type>
 using __enable_if_bullet5 = typename enable_if
     <
         is_member_object_pointer<_DecayFp>::value
         && __is_reference_wrapper<_DecayA0>::value
     >::type;
 
 template <class _Fp, class _A0,
          class _DecayFp = typename decay<_Fp>::type,
          class _DecayA0 = typename decay<_A0>::type,
          class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
 using __enable_if_bullet6 = typename enable_if
     <
         is_member_object_pointer<_DecayFp>::value
         && !is_base_of<_ClassT, _DecayA0>::value
         && !__is_reference_wrapper<_DecayA0>::value
     >::type;
 
 // __invoke forward declarations
 
 // fall back - none of the bullets
 
 template <class ..._Args>
 auto __invoke(__any, _Args&& ...__args) -> __nat;
 
 template <class ..._Args>
 auto __invoke_constexpr(__any, _Args&& ...__args) -> __nat;
 
 // bullets 1, 2 and 3
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet1<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept((static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      (static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...))
     { return          (static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet1<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept((static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      (static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...))
     { return          (static_cast<_A0&&>(__a0).*__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet2<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept((__a0.get().*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      (__a0.get().*__f)(static_cast<_Args&&>(__args)...))
     { return          (__a0.get().*__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet2<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept((__a0.get().*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      (__a0.get().*__f)(static_cast<_Args&&>(__args)...))
     { return          (__a0.get().*__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet3<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept(((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      ((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...))
     { return          ((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class _A0, class ..._Args,
           class = __enable_if_bullet3<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
     noexcept(noexcept(((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      ((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...))
     { return          ((*static_cast<_A0&&>(__a0)).*__f)(static_cast<_Args&&>(__args)...); }
 
 // bullets 4, 5 and 6
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet4<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept(static_cast<_A0&&>(__a0).*__f))
     -> decltype(      static_cast<_A0&&>(__a0).*__f)
     { return          static_cast<_A0&&>(__a0).*__f; }
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet4<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept(static_cast<_A0&&>(__a0).*__f))
     -> decltype(      static_cast<_A0&&>(__a0).*__f)
     { return          static_cast<_A0&&>(__a0).*__f; }
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet5<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept(__a0.get().*__f))
     -> decltype(      __a0.get().*__f)
     { return          __a0.get().*__f; }
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet5<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept(__a0.get().*__f))
     -> decltype(      __a0.get().*__f)
     { return          __a0.get().*__f; }
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet6<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept((*static_cast<_A0&&>(__a0)).*__f))
     -> decltype(      (*static_cast<_A0&&>(__a0)).*__f)
     { return          (*static_cast<_A0&&>(__a0)).*__f; }
 
 template <class _Fp, class _A0,
           class = __enable_if_bullet6<_Fp, _A0>>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _A0&& __a0)
     noexcept(noexcept((*static_cast<_A0&&>(__a0)).*__f))
     -> decltype(      (*static_cast<_A0&&>(__a0)).*__f)
     { return          (*static_cast<_A0&&>(__a0)).*__f; }
 
 // bullet 7
 
 template <class _Fp, class ..._Args>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 auto
 __invoke(_Fp&& __f, _Args&& ...__args)
     noexcept(noexcept(static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...))
     { return          static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...); }
 
 template <class _Fp, class ..._Args>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR auto
 __invoke_constexpr(_Fp&& __f, _Args&& ...__args)
     noexcept(noexcept(static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...)))
     -> decltype(      static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...))
     { return          static_cast<_Fp&&>(__f)(static_cast<_Args&&>(__args)...); }
 
 // __invokable
 template <class _Ret, class _Fp, class ..._Args>
 struct __invokable_r
 {
   template <class _XFp, class ..._XArgs>
   static auto __try_call(int) -> decltype(
     _VSTD::__invoke(declval<_XFp>(), declval<_XArgs>()...));
   template <class _XFp, class ..._XArgs>
   static __nat __try_call(...);
 
   // FIXME: Check that _Ret, _Fp, and _Args... are all complete types, cv void,
   // or incomplete array types as required by the standard.
   using _Result = decltype(__try_call<_Fp, _Args...>(0));
 
   using type =
   typename conditional<
       _IsNotSame<_Result, __nat>::value,
       typename conditional<
           is_void<_Ret>::value,
           true_type,
           is_convertible<_Result, _Ret>
       >::type,
       false_type
   >::type;
   static const bool value = type::value;
 };
 template <class _Fp, class ..._Args>
 using __invokable = __invokable_r<void, _Fp, _Args...>;
 
 template <bool _IsInvokable, bool _IsCVVoid, class _Ret, class _Fp, class ..._Args>
 struct __nothrow_invokable_r_imp {
   static const bool value = false;
 };
 
 template <class _Ret, class _Fp, class ..._Args>
 struct __nothrow_invokable_r_imp<true, false, _Ret, _Fp, _Args...>
 {
     typedef __nothrow_invokable_r_imp _ThisT;
 
     template <class _Tp>
     static void __test_noexcept(_Tp) noexcept;
 
     static const bool value = noexcept(_ThisT::__test_noexcept<_Ret>(
         _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)));
 };
 
 template <class _Ret, class _Fp, class ..._Args>
 struct __nothrow_invokable_r_imp<true, true, _Ret, _Fp, _Args...>
 {
     static const bool value = noexcept(
         _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...));
 };
 
 template <class _Ret, class _Fp, class ..._Args>
 using __nothrow_invokable_r =
     __nothrow_invokable_r_imp<
             __invokable_r<_Ret, _Fp, _Args...>::value,
             is_void<_Ret>::value,
             _Ret, _Fp, _Args...
     >;
 
 template <class _Fp, class ..._Args>
 using __nothrow_invokable =
     __nothrow_invokable_r_imp<
             __invokable<_Fp, _Args...>::value,
             true, void, _Fp, _Args...
     >;
 
 template <class _Fp, class ..._Args>
 struct __invoke_of
     : public enable_if<
         __invokable<_Fp, _Args...>::value,
         typename __invokable_r<void, _Fp, _Args...>::_Result>
 {
 };
 
 #endif // _LIBCPP_CXX03_LANG
 
 // result_of
 
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 template <class _Callable> class _LIBCPP_DEPRECATED_IN_CXX17 result_of;
 
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Fp, class ..._Args>
 class _LIBCPP_TEMPLATE_VIS result_of<_Fp(_Args...)>
     : public __invoke_of<_Fp, _Args...>
 {
 };
 
 #else // C++03
 
 template <class _Fn, bool, bool>
 class __result_of
 {
 };
 
 template <class _Fn, class ..._Args>
 class __result_of<_Fn(_Args...), true, false>
 {
 public:
     typedef decltype(declval<_Fn>()(declval<_Args>()...)) type;
 };
 
 template <class _MP, class _Tp, bool _IsMemberFunctionPtr>
 struct __result_of_mp;
 
 // member function pointer
 
 template <class _MP, class _Tp>
 struct __result_of_mp<_MP, _Tp, true>
 {
     using type = typename __member_pointer_traits<_MP>::_ReturnType;
 };
 
 // member data pointer
 
 template <class _MP, class _Tp, bool>
 struct __result_of_mdp;
 
 template <class _Rp, class _Class, class _Tp>
 struct __result_of_mdp<_Rp _Class::*, _Tp, false>
 {
     using type = typename __apply_cv<decltype(*declval<_Tp>()), _Rp>::type&;
 };
 
 template <class _Rp, class _Class, class _Tp>
 struct __result_of_mdp<_Rp _Class::*, _Tp, true>
 {
     using type = typename __apply_cv<_Tp, _Rp>::type&;
 };
 
 template <class _Rp, class _Class, class _Tp>
 struct __result_of_mp<_Rp _Class::*, _Tp, false>
     : public __result_of_mdp<_Rp _Class::*, _Tp,
             is_base_of<_Class, typename remove_reference<_Tp>::type>::value>
 {
 };
 
 template <class _Fn, class _Tp>
 class __result_of<_Fn(_Tp), false, true>  // _Fn must be member pointer
     : public __result_of_mp<typename remove_reference<_Fn>::type,
                             _Tp,
                             is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
 {
 };
 
 template <class _Fn, class _Tp, class ..._Args>
 class __result_of<_Fn(_Tp, _Args...), false, true>  // _Fn must be member pointer
     : public __result_of_mp<typename remove_reference<_Fn>::type,
                             _Tp,
                             is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
 {
 };
 
 template <class _Fn, class ..._Args>
 class _LIBCPP_TEMPLATE_VIS result_of<_Fn(_Args...)>
     : public __result_of<_Fn(_Args...),
                          is_class<typename remove_reference<_Fn>::type>::value ||
                          is_function<typename remove_pointer<typename remove_reference<_Fn>::type>::type>::value,
                          is_member_pointer<typename remove_reference<_Fn>::type>::value
                         >
 {
 };
 
 #endif // C++03
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using result_of_t _LIBCPP_DEPRECATED_IN_CXX17 = typename result_of<_Tp>::type;
 #endif // _LIBCPP_STD_VER > 11
 #endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 
 #if _LIBCPP_STD_VER > 14
 
 // invoke_result
 
 template <class _Fn, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS invoke_result
     : __invoke_of<_Fn, _Args...>
 {
 };
 
 template <class _Fn, class... _Args>
 using invoke_result_t = typename invoke_result<_Fn, _Args...>::type;
 
 // is_invocable
 
 template <class _Fn, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_invocable
     : integral_constant<bool, __invokable<_Fn, _Args...>::value> {};
 
 template <class _Ret, class _Fn, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_invocable_r
     : integral_constant<bool, __invokable_r<_Ret, _Fn, _Args...>::value> {};
 
 template <class _Fn, class ..._Args>
 inline constexpr bool is_invocable_v = is_invocable<_Fn, _Args...>::value;
 
 template <class _Ret, class _Fn, class ..._Args>
 inline constexpr bool is_invocable_r_v = is_invocable_r<_Ret, _Fn, _Args...>::value;
 
 // is_nothrow_invocable
 
 template <class _Fn, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_invocable
     : integral_constant<bool, __nothrow_invokable<_Fn, _Args...>::value> {};
 
 template <class _Ret, class _Fn, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_invocable_r
     : integral_constant<bool, __nothrow_invokable_r<_Ret, _Fn, _Args...>::value> {};
 
 template <class _Fn, class ..._Args>
 inline constexpr bool is_nothrow_invocable_v = is_nothrow_invocable<_Fn, _Args...>::value;
 
 template <class _Ret, class _Fn, class ..._Args>
 inline constexpr bool is_nothrow_invocable_r_v = is_nothrow_invocable_r<_Ret, _Fn, _Args...>::value;
 
 #endif // _LIBCPP_STD_VER > 14
 
 // __swappable
 
 template <class _Tp> struct __is_swappable;
 template <class _Tp> struct __is_nothrow_swappable;
 
 
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Tp>
 using __swap_result_t = typename enable_if<is_move_constructible<_Tp>::value && is_move_assignable<_Tp>::value>::type;
 #else
 template <class>
 using __swap_result_t = void;
 #endif
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
 _LIBCPP_CONSTEXPR_AFTER_CXX17 __swap_result_t<_Tp>
 swap(_Tp& __x, _Tp& __y) _NOEXCEPT_(is_nothrow_move_constructible<_Tp>::value &&
                                     is_nothrow_move_assignable<_Tp>::value);
 
 template<class _Tp, size_t _Np>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 typename enable_if<
     __is_swappable<_Tp>::value
 >::type
 swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value);
 
 namespace __detail
 {
 // ALL generic swap overloads MUST already have a declaration available at this point.
 
 template <class _Tp, class _Up = _Tp,
           bool _NotVoid = !is_void<_Tp>::value && !is_void<_Up>::value>
 struct __swappable_with
 {
     template <class _LHS, class _RHS>
     static decltype(swap(declval<_LHS>(), declval<_RHS>()))
     __test_swap(int);
     template <class, class>
     static __nat __test_swap(long);
 
     // Extra parens are needed for the C++03 definition of decltype.
     typedef decltype((__test_swap<_Tp, _Up>(0))) __swap1;
     typedef decltype((__test_swap<_Up, _Tp>(0))) __swap2;
 
     static const bool value = _IsNotSame<__swap1, __nat>::value
                            && _IsNotSame<__swap2, __nat>::value;
 };
 
 template <class _Tp, class _Up>
 struct __swappable_with<_Tp, _Up,  false> : false_type {};
 
 template <class _Tp, class _Up = _Tp, bool _Swappable = __swappable_with<_Tp, _Up>::value>
 struct __nothrow_swappable_with {
   static const bool value =
 #ifndef _LIBCPP_HAS_NO_NOEXCEPT
       noexcept(swap(declval<_Tp>(), declval<_Up>()))
   &&  noexcept(swap(declval<_Up>(), declval<_Tp>()));
 #else
       false;
 #endif
 };
 
 template <class _Tp, class _Up>
 struct __nothrow_swappable_with<_Tp, _Up, false> : false_type {};
 
 } // namespace __detail
 
 template <class _Tp>
 struct __is_swappable
     : public integral_constant<bool, __detail::__swappable_with<_Tp&>::value>
 {
 };
 
 template <class _Tp>
 struct __is_nothrow_swappable
     : public integral_constant<bool, __detail::__nothrow_swappable_with<_Tp&>::value>
 {
 };
 
 #if _LIBCPP_STD_VER > 14
 
 template <class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS is_swappable_with
     : public integral_constant<bool, __detail::__swappable_with<_Tp, _Up>::value>
 {
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_swappable
     : public conditional<
         __is_referenceable<_Tp>::value,
         is_swappable_with<
             typename add_lvalue_reference<_Tp>::type,
             typename add_lvalue_reference<_Tp>::type>,
         false_type
     >::type
 {
 };
 
 template <class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_swappable_with
     : public integral_constant<bool, __detail::__nothrow_swappable_with<_Tp, _Up>::value>
 {
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_nothrow_swappable
     : public conditional<
         __is_referenceable<_Tp>::value,
         is_nothrow_swappable_with<
             typename add_lvalue_reference<_Tp>::type,
             typename add_lvalue_reference<_Tp>::type>,
         false_type
     >::type
 {
 };
 
 template <class _Tp, class _Up>
 inline constexpr bool is_swappable_with_v = is_swappable_with<_Tp, _Up>::value;
 
 template <class _Tp>
 inline constexpr bool is_swappable_v = is_swappable<_Tp>::value;
 
 template <class _Tp, class _Up>
 inline constexpr bool is_nothrow_swappable_with_v = is_nothrow_swappable_with<_Tp, _Up>::value;
 
 template <class _Tp>
 inline constexpr bool is_nothrow_swappable_v = is_nothrow_swappable<_Tp>::value;
 
 #endif // _LIBCPP_STD_VER > 14
 
 template <class _Tp, bool = is_enum<_Tp>::value> struct __underlying_type_impl;
 
 template <class _Tp>
 struct __underlying_type_impl<_Tp, false> {};
 
 template <class _Tp>
 struct __underlying_type_impl<_Tp, true>
 {
     typedef __underlying_type(_Tp) type;
 };
 
 template <class _Tp>
 struct underlying_type : __underlying_type_impl<_Tp, is_enum<_Tp>::value> {};
 
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using underlying_type_t = typename underlying_type<_Tp>::type;
 #endif
 
 template <class _Tp, bool = is_enum<_Tp>::value>
 struct __sfinae_underlying_type
 {
     typedef typename underlying_type<_Tp>::type type;
     typedef decltype(((type)1) + 0) __promoted_type;
 };
 
 template <class _Tp>
 struct __sfinae_underlying_type<_Tp, false> {};
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 int __convert_to_integral(int __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 unsigned __convert_to_integral(unsigned __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 long __convert_to_integral(long __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 unsigned long __convert_to_integral(unsigned long __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 long long __convert_to_integral(long long __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 unsigned long long __convert_to_integral(unsigned long long __val) {return __val; }
 
 template<typename _Fp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 typename enable_if<is_floating_point<_Fp>::value, long long>::type
  __convert_to_integral(_Fp __val) { return __val; }
 
 #ifndef _LIBCPP_HAS_NO_INT128
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 __int128_t __convert_to_integral(__int128_t __val) { return __val; }
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 __uint128_t __convert_to_integral(__uint128_t __val) { return __val; }
 #endif
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 typename __sfinae_underlying_type<_Tp>::__promoted_type
 __convert_to_integral(_Tp __val) { return __val; }
 
 // is_scoped_enum [meta.unary.prop]
 
 #if _LIBCPP_STD_VER > 20
 template <class _Tp, bool = is_enum_v<_Tp> >
 struct __is_scoped_enum_helper : false_type {};
 
 template <class _Tp>
 struct __is_scoped_enum_helper<_Tp, true>
     : public bool_constant<!is_convertible_v<_Tp, underlying_type_t<_Tp> > > {};
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_scoped_enum
     : public __is_scoped_enum_helper<_Tp> {};
 
 template <class _Tp>
 inline constexpr bool is_scoped_enum_v = is_scoped_enum<_Tp>::value;
 #endif
 
 #if _LIBCPP_STD_VER > 14
 
 template <class... _Args>
 struct conjunction : _And<_Args...> {};
 template<class... _Args>
 inline constexpr bool conjunction_v = conjunction<_Args...>::value;
 
 template <class... _Args>
 struct disjunction : _Or<_Args...> {};
 template<class... _Args>
 inline constexpr bool disjunction_v = disjunction<_Args...>::value;
 
 template <class _Tp>
 struct negation : _Not<_Tp> {};
 template<class _Tp>
 inline constexpr bool negation_v = negation<_Tp>::value;
 #endif // _LIBCPP_STD_VER > 14
 
 // These traits are used in __tree and __hash_table
 struct __extract_key_fail_tag {};
 struct __extract_key_self_tag {};
 struct __extract_key_first_tag {};
 
 template <class _ValTy, class _Key,
           class _RawValTy = typename __unconstref<_ValTy>::type>
 struct __can_extract_key
     : conditional<_IsSame<_RawValTy, _Key>::value, __extract_key_self_tag,
                   __extract_key_fail_tag>::type {};
 
 template <class _Pair, class _Key, class _First, class _Second>
 struct __can_extract_key<_Pair, _Key, pair<_First, _Second> >
     : conditional<_IsSame<typename remove_const<_First>::type, _Key>::value,
                   __extract_key_first_tag, __extract_key_fail_tag>::type {};
 
 // __can_extract_map_key uses true_type/false_type instead of the tags.
 // It returns true if _Key != _ContainerValueTy (the container is a map not a set)
 // and _ValTy == _Key.
 template <class _ValTy, class _Key, class _ContainerValueTy,
           class _RawValTy = typename __unconstref<_ValTy>::type>
 struct __can_extract_map_key
     : integral_constant<bool, _IsSame<_RawValTy, _Key>::value> {};
 
 // This specialization returns __extract_key_fail_tag for non-map containers
 // because _Key == _ContainerValueTy
 template <class _ValTy, class _Key, class _RawValTy>
 struct __can_extract_map_key<_ValTy, _Key, _Key, _RawValTy>
     : false_type {};
 
 #if _LIBCPP_STD_VER > 17
 _LIBCPP_INLINE_VISIBILITY
 inline constexpr bool is_constant_evaluated() noexcept {
   return __builtin_is_constant_evaluated();
 }
 #endif
 
 inline _LIBCPP_CONSTEXPR
 bool __libcpp_is_constant_evaluated() _NOEXCEPT { return __builtin_is_constant_evaluated(); }
 
 template <class _CharT>
 using _IsCharLikeType = _And<is_standard_layout<_CharT>, is_trivial<_CharT> >;
 
 template<class _Tp>
 using __make_const_lvalue_ref = const typename remove_reference<_Tp>::type&;
 
 #if _LIBCPP_STD_VER > 17
 template<bool _Const, class _Tp>
 using __maybe_const = conditional_t<_Const, const _Tp, _Tp>;
 #endif // _LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_TYPE_TRAITS