Sophie Spirkl: A counterexample to a conjecture about triangle-free induced subgraphs of graphs with large chromatic number

Abstract: I will present a counterexample to the following well-known conjecture: for every k, r, every graph G with clique number at most k and sufficiently large chromatic number contains a triangle-free induced subgraph with chromatic number at least r. I will also discuss some related results (including the construction of Brianski, Davies, and Walczak disproving Esperet's conjecture on polynomial chi-boundedness). Based on joint work with Alvaro Carbonero, Patrick Hompe, and Ben Moore.