Hi all, I'm currently fixing up leda_graph.hpp so it passes the tests, or indeed, fixing the tests ... A leda::GRAPH<int,int> (=Graph) has to fulfill VertexListGraphConcept. This means that boost::graph_traits<G>::vertex_iterator has to be a MultiPassInputIterator, i.e., also a InputIterator. I cannot read from http://www.sgi.com/tech/stl/InputIterator.html that it must be possible that you can compute the difference between two iterators. But apparently the concept check (which fails) requires a difference type, which must be a signed integer. Is this a bug in the concept check? The vertex_iterator type is defined in leda_graph.hpp using iterator_facade: class vertex_iterator : public iterator_facade<vertex_iterator, leda::node, bidirectional_traversal_tag, const leda::node&, const leda::node*> { public: vertex_iterator(leda::node node = 0, const leda::GRAPH<vtype, etype>* g = 0) : base(node), g(g) {} private: const leda::node& dereference() const { return base; } bool equal(const vertex_iterator& other) const { return base == other.base; } void increment() { base = g->succ_node(base); } void decrement() { base = g->pred_node(base); } leda::node base; const leda::GRAPH<vtype, etype>* g; friend class iterator_core_access; }; Is maybe iterator_facade insufficient? For me, bidirectional_traversal_tag does not indicate that random access is possible ... -- Jens