Hi! I am using a graph with setS as EdgeList template-parameter. I currently try to implement to get the number of neighbors which two vertices have in common. I tried to solve this problem by walking thought both out_edge_iterator - ranges in parallel. tie( i, i_end ) = out_edges( vertex_i, graph ); tie( j, j_end ) = out_edges( vertex_j, graph ); int a =0; for( ;; ) { if( *i == *j ) { ++i; ++j; ++a; if( i == iend ) return a; if( j == jend ) return a; } else if( *i < *j ) { // PROBLEM ++i; if( i == iend ) return a; } else /* ( *i > *j ) */ { ++j; if( j == jend ) return a; }; }; return 0; }; And get the following error message: ../../../pocket_graph/src/clustering/GraphAssociation.h:147: error: no match for 'operator<' in 'boost::iterator_facade<I, V, TC, R, D>::operator*() const [with Derived = Which basicaly tells me that operator< is not defined for an edge descriptor. After digging through some bgl-code I found the class stored_edge (in detail/adjacency_list.hpp ) template <class Vertex> class stored_edge : public boost::equality_comparable1< stored_edge<Vertex>, boost::less_than_comparable1< stored_edge<Vertex> > > { public: typedef no_property property_type; inline stored_edge() { } inline stored_edge(Vertex target, const no_property& = no_property()) : m_target(target) { } // Need to write this explicitly so stored_edge_property can // invoke Base::operator= (at least, for SGI MIPSPro compiler) inline stored_edge& operator=(const stored_edge& x) { m_target = x.m_target; return *this; } inline Vertex& get_target() const { return m_target; } inline const no_property& get_property() const { return s_prop; } inline bool operator==(const stored_edge& x) const { return m_target == x.get_target(); } inline bool operator<(const stored_edge& x) const { return m_target < x.get_target(); } //protected: need to add hash<> as a friend static no_property s_prop; // Sometimes target not used as key in the set, and in that case // it is ok to change the target. mutable Vertex m_target; }; for some reason I can not use operator<() or get_target(), but accessing m_target directly works (cause its mutable???)... } else if( i->m_target < j->m_target ) { // SOLUTION ?! However - I feel a bit uneasy to use such a low level interface... Does anyone know of a better solution? Thanks for your help! Lars