see https://en.wikipedia.org/wiki/Bulls_and_cows

https://www.jsoftware.com/papers/50/50_27.htm

https://en.wikipedia.org/wiki/Mastermind_(board_game)

https://archive.org/details/h42_DECUS_8-394/page/n3/mode/2up

https://www.singlix.com/trdos/archive/pdf_archive/unix_v1_programmers_manual.pdf

https://ia903204.us.archive.org/7/items/vax-sysv/man/catman.txt/u_man/man6/moo.6.txt

https://github.com/hansklav/MOO

https://web.archive.org/web/20161106163203/http://ftp.stratus.com/vos/multics/pg/moo.pl1

https://www.cs.uni.edu/~wallingf/teaching/cs3530/resources/knuth-mastermind.pdf

https://www.messforless.net/what-is-the-bagel-pico-fermi-math-game/

https://www.vice.com/en/article/permalink-mastermind-board-game-50th-anniversary-origins-fallout-cybersecurity/

https://onlinelibrary.wiley.com/doi/10.1002/spe.4380010210

https://stackoverflow.com/questions/67960248/bulls-and-cows-turning-simple-code-into-functions

https://github.com/justforthefunofit/small-basic-examples/blob/main/mastermind.bas

https://web.archive.org/web/20120425120039/http://www.jfwaf.com/Bulls%20and%20Cows.pdf

https://codebreaker-mastermind-superhirn.blogspot.com/2012/07/bulls-and-cows-mastermind-superhirn.html

https://www.multicians.org/moo-in-multics-1972.pdf

https://www.wikihow.com/Play-Mastermind
