Lower bounds for the colored mixed chromatic number of some classes of graphs
A colored mixed graph has vertices linked by both colored arcs and colored edges. The chromatic number of such a graph is defined as the smallest order of a colored mixed graph such that there exists a (color preserving) homomorphism from to . These notions were introduced by Nešetřil and Raspaud in , J. Combin. Theory Ser. B (2000), no. 1, 147–155, where the exact chromatic number of colored mixed trees was given. We prove here that this chromatic number is reached by the much simpler family...