typedef typename Parent::Node Node;

     class UndirIncEdgeIt : public UndirEdge { 

       const Graph* graph;

       bool forward;

       friend class IterableUndirGraphExtender;

       template <typename G>

       friend class UndirGraphExtender;

     public:

       UndirIncEdgeIt() { }

       UndirIncEdgeIt(Invalid i) : UndirEdge(i), forward(false) { }

       explicit UndirIncEdgeIt(const Graph& _graph, const Node &n)

 	: graph(&_graph)

       {

 	_graph._dirFirstOut(*this, n);

       }

       // FIXME: Do we need this type of constructor here?

       // UndirIncEdgeIt(const Graph& _graph, const UndirEdge& e) : 

       //   UndirEdge(e), graph(&_graph) { }

       UndirIncEdgeIt& operator++() {

 	graph->_dirNextOut(*this);

 	return *this; 

       }

     };

     Node source(const UndirIncEdgeIt &e) const {

       return _dirSource(e);

     }

     /// \todo Shouldn't the "source" of an undirected edge be called "aNode"

     /// or something???

     using Parent::source;

     /// Target of the given Edge.

     Node target(const UndirIncEdgeIt &e) const {

       return _dirTarget(e);

     }

     /// \todo Shouldn't the "target" of an undirected edge be called "bNode"

     /// or something???

     using Parent::target;