Hello, I want an undirected graph with non-multiple edges. So I use a graph defined as : adjacencylist<setS,vecS,undirectedS,SomeProperty> But, if I insert many times the same edge with: add_edge(2,3) add_edge(1,4) add_edge(2,3) add_edge(3,2) I obtain in fact 3 edges 2<->3 which I really don't want. Is there something else to do to avoid having multiple edges linking the same vertices ? And then, is there a way to user hash_set with g++-3.2 ? The problem being that hash_set is defined in the file ext/hash_set and in the namespace __gnu_cxx ... Thanks, -- Pierre Barbier de Reuille INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP Botanique et Bio-informatique de l'Architecture des Plantes TA40/PSII, Boulevard de la Lironde 34398 MONTPELLIER CEDEX 5, France tel : (33) 4 67 61 65 77 fax : (33) 4 67 61 56 68