Heavy subgraphs, stability and Hamiltonicity
Binlong Li, Bo Ning · Discussiones Mathematicae Graph Theory · 2017
Let G be a graph. Adopting the terminology of Broersma et al. and ada, respectively, we say that G is 2-heavy if every induced claw (K 1,3 ) of G contains two end-vertices each one has degree at least |V (G)|/2; and G is o-heavy if every induced claw of G contains two end-vertices with degree sum at least |V (G)| in G. In this paper, we introduce a new concept, and say that G is S-c-heavy if for a given graph S and every induced subgraph G of G isomorphic to S and every maximal clique C of G , every nontrivial component of G -C contains a vertex of degree at least |V (G)|/2 in G. Our original motivation is a theorem of Hu from 1999 that can be stated, in terms of this concept, as every 2-connected 2-heavy and N -cheavy graph is hamiltonian, where N is the graph obtained from a triangle by adding three disjoint pendant edges. In this paper, we will characterize all connected graphs S such that every 2-connected o-heavy and S-c-heavy graph is hamiltonian. Our work results in a different proof of a stronger version of Hu's theorem. Furthermore, our main result improves or extends several previous results.