Another interesting and related topic are Ramsey numbers. R(3,3)=6 which means: "In any party of six people either at least three of them are (pairwise) mutual

Another interesting and related topic are Ramsey numbers. R(3,3)=6 which means: "In any party of six people either at least three of them are (pairwise) mutual strangers or at least three of them are (pairwise) mutual acquaintances" https://en.wikipedia.org/wiki/Theorem_on_friends_and_strangers https://en.wikipedia.org/wiki/Theorem_on_friends_and_strange...