Markov Equivalent Class Graph

A Markov equivalence class can be represented by a graph with
1. Same link and
2. Same uncoupled head-to-head meetings
Any assignment of directions to the undirected edges in this graph, that does not create a new uncoupled head-to-head meeting or a directed cycle, yields a member of the equivalence class.

(Find detail on http://mmc36.informatik.uni-augsburg.de/mediawiki/data/3/3a/SS07_MM2_Lec06-Bayesian_Networks_chapter02_Part2.pdf )