Fan-type degree condition restricted to triples of induced subgraphs ensuring Hamiltonicity

Abstract

In 1984, Fan gave a sufficient condition involving maximum degree of every pair of vertices at distance two for a graph to be Hamiltonian. Motivated by Fan's result, we say that an induced subgraph $H$ of a graph $G$ is $f$-heavy if for every pair of vertices $u,v\in V(H)$, $d_H(u,v)=2$ implies that $\max \{d(u),d(v)\}\ge n/2$. For a given graph $R$, $G$ is called $R$-$f$-heavy if every induced subgraph of $G$ isomorphic to $R$ is $f$-heavy. For a family $\mathcal{R}$ of graphs, $G$ is $\mathcal{R}$-$f$-\emph{heavy} if $G$ is $R$-$f$-heavy for every $R\in \mathcal{R}$. In this note we show that every 2-connected graph $G$ has a Hamilton cycle if $G$ is $\{K_{1,3},P_7,D\}$-$f$-heavy or $\{K_{1,3},P_7,H\}$-$f$-heavy, where $D$ is the deer and $H$ is the hourglass. Our result is a common generalization of previous theorems of Broersma et al. and Fan on Hamiltonicity of 2-connected graphs.

8 pages, 1 figure