On N2N2-vertex coloring of graphs
Abstract
Let G be a graph. A vertex coloring ψ of G is called N2-vertex coloring if |ψ(v)|≤2 for every vertex v of G, where ψ(v) is the set of colors of vertices adjacent to v. Let t2(G) be the maximum number of colors used in an N2-vertex coloring of G. We provide some lower and upper bounds for t2(G) in terms of girth, diameter or size of G. Also, for every tree T, we obtain t2(T).