The f-Chromatic Index of a Graph Whose f-Core Has Maximum Degree 2

Abstract

Abstract.Let G be a graph. The minimum number of colors needed to color the edges of G is called the chromatic index of G and is denoted by χ'(G). It is well known that , for any graph G, where Δ(G) denotes the maximum degree of G. A graph G is said to be class 1 if x'(G) = Δ(G) and class 2 if χ'(G) = Δ(G)+1. Also, GΔ is the induced subgraph on all vertices of degree Δ(G). Let f : V(G) → ℕ be a function. An f-coloring of a graph G is a coloring of the edges of E(G) such that each color appears at each vertex v ∊ V(G) at most f (v) times. The minimum number of colors needed to f-color G is called the f-chromatic index of G and is denoted by χ'f (G). It was shown that for every graph , where . A graph G is said to be f -class 1 , and f -class 2, otherwise. Also, GΔf is the induced subgraph of G on . Hilton and Zhao showed that if G has maximum degree two and G is class 2, then G is critical, GΔ is a disjoint union of cycles and δ(G) = Δ(G)–1, where δ(G) denotes the minimum degree of G, respectively. In this paper, we generalize this theorem to f -coloring of graphs. Also, we determine the f -chromatic index of a connected graph G with |GΔf| ≤ 4.