  bool contained_in_boundary(Object_handle h) const
  /*{\Mop  returns true iff the object |h| is contained in the $1$-skeleton
  of |\Mvar|.}*/
  { Vertex_const_handle v;
    Halfedge_const_handle e;
    return  ( CGAL::assign(v,h) || CGAL::assign(e,h) );
  }
  bool contained_in_boundary(Object_handle h) const
   
  { Vertex_const_handle v;
    Halfedge_const_handle e;
    return  ( CGAL::assign(v,h) || CGAL::assign(e,h) );
  }