Cograph
![The Turán graph T(13,4), an example of a cograph](/Images/godic/202501/06/Turan_13-4.svg3952.png")
![A cotree and the corresponding cograph. Each edge (u,v) in the cograph has a matching color to the least common ancestor of u and v in the cotree.](/Images/godic/202501/06/Cotree_and_cograph.svg3952.png")
In graph theory, a cograph, or complement-reducible graph, or P4-free graph, is a graph that can be generated from the single-vertex graph K1 by complementation and disjoint union. That is, the family of cographs is the smallest class of graphs that includes K1 and is closed under complementation and disjoint union.