In graph theory, the class of cographs (or complement-reducible graphs, or P4-free graphs) is the smallest class of graphs including the single vertex graph K_1 and closed under complement and disjoint union.
In graph theory, the class of cographs (or complement-reducible graphs, or P4-free graphs) has been introduced by Seinsche in 1974. It is the smallest class of graphs including the single vertex graph K_1 and closed under complement and disjoint union.