OK, I have a somewhat unrelated question. (I think I can modify the Boost algorithm to do what I want.) In libs/graph/example/isomorphism.hpp, if I change undirectedS to bidirectionalS, then the answer changes from the two graphs being isomorphic to not. (It then proceeds to segfault when looking at the isomorphism map.) typedef adjacency_list<vecS, listS, undirectedS, property<vertex_index_t, int> > graph_t; to typedef adjacency_list<vecS, listS, bidirectionalS, property<vertex_index_t, int> > graph_t; Why is this? Near as I can tell, the graphs should be isomorphic. Graph 1 has three cycles, 0->1->2->0, 3->4->5->6->3, and 7->8->9->10->11->7. Graph 2 has three cycles of the same sizes, 9->10->11->9, 0->1->3->2->0, and 4->5->7->8->6->4. (These are all the transitions.) Evan Driscoll