[Boost-users] BGL - edge descriptor and map

I'd like to specify better my problem. I'd like to use an edge_descriptor (graph_traits<G>::edge_descriptor) as key in a map. The graph type is something like this: typedef adjacency_list G; I think that I've to overload the < operator for graph_traits<G>::edge_descriptor. Is this correct? If so, given two edge_descriptors I need to access the source and the target of the edge in such a way to define a sort ordering. Thanks, Giulio