On incidence coloring conjecture in Cartesian products of graphs

An incidence in a graph G is a pair (v, e) where v is a vertex of G and e is an edge of G incident to v. Two incidences (v, e) and (u, f) are adjacent if at least one of the following holds: (a) v = u, (b) e = f, or (c) vu is an element of {e, f}. An incidence coloring of G is a coloring of its incidences assigning distinct colors to adjacent incidences. It was conjectured that at most Delta(G) + 2 colors are needed for an incidence coloring of any graph G. The conjecture is false in general, but the bound holds for many classes of graphs. We introduce some sufficient properties of the two factor graphs of a Cartesian product graph G for which G admits an incidence coloring with at most Delta(G) + 2 colors. (C) 2016 Elsevier B.V. All rights reserved.