```
core(5) appeared in Version 1 AT&T UNIX
https://www.bell-labs.com/usr/dmr/www/man51.pdf
Obtained from: NetBSD
```
Found it here: https://freshbsd.org/commit/netbsd/src/C72SdP9c4uqCJgCB
https://www.bell-labs.com/usr/dmr/www/man51.pdf is a scan of the manual for the first edition of UNIX as explained here: https://www.bell-labs.com/usr/dmr/www/1stEdman.html