… ..
http://en.wikipedia.org/wiki/PQ_tree
http://en.wikipedia.org/wiki/Planarity_testing
http://en.wikipedia.org/wiki/Interval_graph
http://en.wikipedia.org/wiki/Doubly_connected_edge_list OOrz
http://ipsc.ksp.sk/contests/ipsc2002/real/problems/d.php
http://acm.hust.edu.cn:8080/judge/problem/viewProblem.action?id=18698
… . . . .. .
http://www.jharris.ca/portfolio/code/pqtree/PQTree.html OOrz
