/// Gives back the stored edge references.

     /// Gives back the stored edge references.

     const EdgeRefMap& edgeRef() const {

     const EdgeRefMap& edgeRef() const {

       return edgeRefMap;

       return edgeRefMap;

     }

     }

   private:

   private:

     const Source& source;

     const Source& source;

     Target& target;

     Target& target;

     /// Gives back the stored uedge references.

     /// Gives back the stored uedge references.

     const UEdgeRefMap& uEdgeRef() const {

     const UEdgeRefMap& uEdgeRef() const {

       return uEdgeRefMap;

       return uEdgeRefMap;

     }

     }

   private:

   private:

     const Source& source;

     const Source& source;

     Target& target;

     Target& target;