图G的一个k-边染色是一个映射φ:E(G)→{1,2,…k),使得每一对相邻边x和y,有φ(x)≠φ(y).G的边色数x′(G)是使得G有一个k-边染色的最小的整数k.本文证明了:如果G是一个最大度为6能嵌入到欧拉示性数非负的曲面的图,且满足下列条件之一,那么x′(G)=6:(1)不含带弦4-圈;(2)同时不含带弦5-圈和带弦6-圈.
A k-edge coloring of a graph G is a mapping φ from E(G) to the color set (1, 2,..., k) such that any two adjacent edges have different colors. The chromatic index X'(G) is the smallest integer k such that G admits a k-edge coloring. In this paper, we prove that every graph G with maximum degree 6 which is embeddable in a surface of nonegative Euler characteristic has X'(G) = 6 if either G has no 4-cycle with a chord, or G has no 5- and 6-cycle with a chord.