Sperner's lemma

Sperner's lemma is a combinatorial statement about some colorings of the triangulations of a triangle. It can be used to prove the Brouwer fixed point theorem.

Bhavik and I had a go at implementing Sperner's lemma in Lean 3 back in 2021 (in fact, Bhavik had an even earlier go). We reduced the problem to some combinatorial statement with geometric input, and found a proof of it, but the effort petered out before that proof was formalised.

I would be happy to supervise someone to take over where we left things off.