A short proof of w_1^n(Hom(C_{2r+1}, K_{n+2}))=0 for all n and a graph colouring theorem by Babson and Kozlov
Abstract
Description
We show that the n-th power of the first Stiefel-Whitney class of the Z_2-operation on the graph complex Hom(C_{2r+1},K_{n+2})$ is zero, confirming a conjecture by Babson and Kozlov. This proves the strong form of their graph colouring theorem, which they had only proven for odd n. Our proof is also considerably simpler than their proof of the weak form of the theorem, which is also known as the Lovász conjecture.
slight simplification of the proof, updated references
slight simplification of the proof, updated references