What is "cograph"

n. (context mathematics English) A graph formed from another by complementation and disjoin union

In graph theory, a cograph, or complement-reducible graph, or P-free graph, is a graph that can be generated from the single-vertex graph K by complementation and disjoint union. That is, the family of cographs is the smallest class of graphs that includes K and is closed under complementation and disjoint union.

Cographs have been discovered independently by several authors since the 1970s; early references include , , , and . They have also been called D*-graphs, hereditary Dacey graphs (after the related work of James C. Dacey Jr. on orthomodular lattices), and 2-parity graphs. They have a simple structural decomposition involving disjoint union and complement graph operations that can be represented concisely by a labeled tree, and used algorithmically to efficiently solve many problems such as finding the maximum clique that are hard on more general graph classes.

Special cases of the cographs include the complete graphs, complete bipartite graphs, cluster graphs, and threshold graphs. The cographs are, in turn, special cases of the distance-hereditary graphs, comparability graphs, and perfect graphs.