I just noticed that the online docs for DFS mention the tree edge/back edge ambiguity, though it looks like that didn't get into the BGL book. http://www.boost.org/libs/graph/doc/depth_first_search.html BTW, the solution suggested in the online docs (recording predecessors) only words for graphs without parallel edges. A more general approach is to mark the edges themselves as I suggested in the previous email. Regards, Jeremy ---------------------------------------------------------------------- Jeremy Siek http://php.indiana.edu/~jsiek/ Ph.D. Student, Indiana Univ. B'ton email: jsiek@osl.iu.edu C++ Booster (http://www.boost.org) office phone: (812) 855-3608 ----------------------------------------------------------------------