[Boost-users] [BGL] IncidenceGraph and out_edges

Hello, I do a repost here because of a silly subject copy and paste error of me, sorry for that! The text of my original message is: I'm trying to implement the IncidenceGraph concept for an non-BGL undirected graph like datastructure. Following the boost documentation the target function used with edges from out_edges(u,g) must give vertices != u. Can somebody please explain me why this requirement is in BGL! I think it can make the adaption very difficult as it requieres to artificially orientate undirected edges for each call to out_edges. Any help would be much appreciated! best regards, Chris