1. Cole, C. 1987. Feynman's cipher. https://groups.google.com/g/sci.crypt/c/u1O1W1mL7Fw
2. Dunin, E. 2003. Famous unsolved codes and ciphers. https://elonka.com/UnsolvedCodes.html
3. Feynman "Olum I" Cipher. 2019. https://www.reddit.com/r/codes/comments/b69ovn/feynman_olum_i_cipher/
4. Feynman "Olum II" Cipher. 2019. https://www.reddit.com/r/codes/comments/b69xtq/feyman_olum_ii_cipher/