Bounds for B-coloring planar and outerplanar graphs

Abstract

A proper coloring of the edges of a graph is one in which every $K_{1,2}$ is totally multicolored. A B-coloring is a coloring of the edges of $G$ in which every $K_{1,2}$ and every $K_{2,2}$ is totally multicolored. In this paper, we improve two results by the authors and Gyárfás. The first shows that an outerplanar graph with maximum degree $Δ$ can be B-colored with $\max\{Δ,9\}$ colors, improving a bound of $Δ+1$ and this is best possible up to the constant 9. The second shows that a planar graph with maximum degree $Δ$ can be B-colored with $\max\{2Δ+4,22\}$, improving a bound of $2Δ+8$.