The Four-Color Theorem 1852–1976

Professor Appel was my boss when I was a system administrator for the UIUC Math department, working my way through grad school. He was one of the best bosses I’ve had over the past thirty years and had a real knack for dealing with the immature twenty something’s (like me).

He was incredibly humble about the 4 color proof, and well, just about everything. He continued to learn new things — I remember him asking me to help him debug some PostScript and I couldn’t believe it was happening.

Fantastic read. The OP does a great job of describing how gradual progress occurs in mathematics. Thank you for sharing this on HN.

Deep down, I'm still hoping someone or something will find a beautiful proof that is more elegant than brute-force counting and verifying that four colors suffice for all unavoidable configurations that reduce to all other possible configurations. According to the article, there are 633 of those configurations. No idea if a more elegant proof is possible, but I hope it is.

A proof of this theorem was also formalized in the Rocq proof assistant (called Coq back then). See here for more: https://inria.hal.science/hal-04034866/document