Generalizing Cographs to 2-Cographs

TL;DR

This paper introduces 2-cographs, a generalization of cographs, characterizes their properties, and explores their closure under induced minors, expanding the understanding of graph classes related to connectivity and minors.

Contribution

The paper defines 2-cographs, proves their recursive structure, and characterizes their minimal non-members and their complements, extending cograph theory to a broader class.

Findings

2-cographs are recursively definable.

They are closed under induced minors.

Characterization of minimal non-2-cographs and their complements.

Abstract

A graph in which every connected induced subgraph has a disconnected complement is called a cograph. Such graphs are precisely the graphs that do not have the 4-vertex path as an induced subgraph. We define a $2$-cograph to be a graph in which the complement of every $2$-connected induced subgraph is not $2$-connected. We show that, like cographs, $2$-cographs can be recursively defined. But, unlike cographs, $2$-cographs are closed under induced minors. We characterize the class of non-$2$-cographs for which every proper induced minor is a $2$-cograph. We further find the finitely many members of this class whose complements are also induced-minor-minimal non-$2$-cographs.