On pre-Hamiltonian cycles in balanced bipartite digraphs

Abstract

Let $D$ be a strongly connected balanced bipartite directed graph of order $2a\ge 10$. Let $x,y$ be distinct vertices in $D$. $\{x,y\}$ dominates a vertex $z$ if $x\to z$ and $y\to z$; in this case, we call the pair $\{x,y\}$ dominating. In this paper we prove: {\it If the underlying undirected graph of $D$ is not 2-connected and $max\{d(x),d(y)\}\ge 2a-2$ for every dominating pair of vertices $\{x,y\}$, then $D$ contains a cycle of length $2a-2$ unless $D$ is isomorphic to a certain digraph of order ten which we specify.

10 pages