Algorithms for Perfectly Contractile Graphs
Frédéric Maffray, Nicolas Trotignon · SIAM Journal on Discrete Mathematics · 2005
We consider the class ${\cal A}$ of graphs that contain no odd hole, no antihole of length at least 5, and no prism (a graph consisting of two disjoint triangles with three disjoint paths between them) and the class ${\cal A}'$ of graphs that contain no odd hole, no antihole of length at least 5, and no odd prism (prism whose three paths are odd). These two classes were introduced by Everett and Reed and are relevant to the study of perfect graphs. We give polynomial-time recognition algorithms for these two classes. In contrast we prove that determining if a general graph contains a prism (or an even prism, or an odd prism) is NP-complete.