Requiring adjacent chords in cycles

Abstract

Define a new class of graphs by cycles of length 5 or more always having adjacent chords. This is equivalent to cycles of length 5 or more always having noncrossing chords, which is a property that has a known forbidden induced subgraph characterization. Another characterization comes from viewing the graphs in this class in contrast to distance-hereditary graphs (which are characterized by cycles of length 5 or more always having crossing chords). Moreover, the graphs in the new class are those in which every edge of every cycle [Formula: see text] of length 5 or more forms a triangle with a third vertex of [Formula: see text] (generalizing that a graph is chordal if and only if every edge of every cycle [Formula: see text] of length 4 or more forms a triangle with a third vertex of [Formula: see text]). This leads to a strategically-required subgraph characterization of the new class.