File:List-coloring-K-3-27.svg

English: An instance of the list coloring problem, on the complete bipartite graph K_3,27, with three colors per vertex. No matter which colors are chosen for the three central vertices, one of the 27 outer vertices will have all of its three colors used by its three neighbors, preventing it from being colored. Therefore, the list chromatic number of K_3,27 is at least four.