Hi folks! I got a cyclic type-dependency problem. I am trying to let every vertex store a iterator to a list which stores vertex-iterators. This sounds weired, but I need to keep track of very few vertices within my graph which have a particle located at it. Thus I created a list of vertex-iterators who carry my particle positions in the graph. In order to be able to tell quickly if a vertice is taken by a particle I want each vertice to include a pointer to a null element representing the absence of a particle or a pointer into that list. My non-working code looks like: Definition of my graph: struct Spot { // acutally I need the vertex_iterator to be defined already // in order to define particle, but this is not yet defined // so I am using the knowledge that it is going to be represented // by a vector<std::size_t>::iterator (at least I hope so) // this assumption is WRONG!! typedef std::list< std::vector<std::size_t>::iterator >::iterator \\ particle_t; particle_t particle; }; typedef boost::adjacency_list<boost::vecS, boost::vecS, \\ boost::undirectedS, Spot > graph_t; Here I initialise my particles to be distributed in the graph object bg. m_posA is of type: std::list<RandomGraph::gtraits::vertex_iterator> // first initialise every position to the null-flag for(; vi != vend; ++vi) bg[*vi].particle = Spot::particle_t(); // now place particles at random positions boost::tie(vi, vend) = boost::vertices(bg); for(std::size_t i = 0; i < initialA; i++) { std::size_t pos; //aList_t::iterator iter; // find a random empty vertice do { pos = rand_gen(); } while(bg[pos].particle != m_posA_end); // place particle A there RandomGraph::gtraits::vertex_iterator vref = vi + pos; // put returns an iterator to the list-element where // vref has been stored bg[pos].particle = m_posA.put(vref); } Any help would be great. Thanks in adavance. Greetings, Sebastian Weber