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Edge degrees and dominating cycles
Authors:Kiyoshi Yoshimoto
Institution:Department of Mathematics, College of Science and Technology, Nihon University, Tokyo 101-8308, Japan
Abstract:The edge degree d(e) of the edge e=uv is defined as the number of neighbours of e, i.e., |N(u)∪N(v)|-2. Two edges are called remote if they are disjoint and there is no edge joining them. In this article, we prove that in a 2-connected graph G, if d(e1)+d(e2)>|V(G)|-4 for any remote edges e1,e2, then all longest cycles C in G are dominating, i.e., G-V(C) is edgeless. This lower bound is best possible.As a corollary, it holds that if G is a 2-connected triangle-free graph with σ2(G)>|V(G)|/2, then all longest cycles are dominating.
Keywords:Dominating cycle  Edge degree  Triangle-free graph  Longest cycle
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