Completed partially directed acyclic graph

The completed partially directed acyclic graph of a Markov equivalence of directed acyclic graphs class has their common skeleton of a directed graph. An edge is directed exactly when its orientation agrees in every member of the class, and is otherwise undirected. It can be constructed by enumerating all acyclic orientations with the prescribed unshielded colliders and retaining only the common directions; practical PC algorithms use orientation propagation instead of enumeration.