Published by the Department of Computer Science, The University of Chicago.
A class of graphs is Kruskalian if Kruskal's theorem on a well-quasi-ordering of finite trees provides a finite characterization in terms of forbidden induced subgraphs. Let k be a natural number. A graph is a k-cograph if its vertices can be colored with colors from the set {1,...,k} such that for every nontrivial subset of vertices W there exists a partition W_1,W_2 of W into nonempty subsets such that either no vertex of W_1 is adjacent to a vertex of W_2 or, such that there exists a permutation pi of k elements such that vertices with color i in W_1 are adjacent exactly to the vertices with color pi(i) in W_2, for all i in {1, ... k}. We prove that k-cographs are Kruskalian. We show that k-cographs have bounded rankwidth and that they can be recognized in O(n^3) time.