  Nef_polyhedron_2(const Plane_map& H, bool clone=true) : Base(Nef_rep())
  /*{\Xcreate makes |\Mvar| a new object.  If |clone==true| then the
  underlying structure of |H| is copied into |\Mvar|.}*/
  { if (clone) {
      Decorator D(pm()); // a decorator working on the rep plane map
      D.clone(H);        // cloning H into pm()
    }
  }
  Nef_polyhedron_2(const Plane_map& H, bool clone=true) : Base(Nef_rep())
   
  { if (clone) {
      Decorator D(pm());  
      D.clone(H);         
    }
  }