template <typename _Base>

   class ClearableUndirBipartiteGraphExtender : public _Base {

   public:

     typedef _Base Parent;

     typedef ClearableUndirBipartiteGraphExtender Graph;

     typedef typename Parent::Node Node;

     typedef typename Parent::LowerNode LowerNode;

     typedef typename Parent::UpperNode UpperNode;

     typedef typename Parent::Edge Edge;

     typedef typename Parent::UndirEdge UndirEdge;

     void clear() {

       Parent::getNotifier(Edge()).clear();

       Parent::getNotifier(UndirEdge()).clear();

       Parent::getNotifier(Node()).clear();

       Parent::getNotifier(LowerNode()).clear();

       Parent::getNotifier(UpperNode()).clear();

       Parent::clear();

     }

   };