  Nef_polyhedron_2(Content plane = EMPTY) : Base(Nef_rep())
  /*{\Mcreate creates an instance |\Mvar| of type |\Mname|
  and initializes it to the empty set if |plane == EMPTY|
  and to the whole plane if |plane == COMPLETE|.}*/
  {
    ES_list L;
    fill_with_frame_segs(L);
    Overlayer D(pm());
    Link_to_iterator I(D, --L.end(), false);
    D.create(L.begin(),L.end(),I);
    D.mark(--D.faces_end()) = bool(plane);
  }
  Nef_polyhedron_2(Content plane = EMPTY) : Base(Nef_rep())
   
  {
    ES_list L;
    fill_with_frame_segs(L);
    Overlayer D(pm());
    Link_to_iterator I(D, --L.end(), false);
    D.create(L.begin(),L.end(),I);
    D.mark(--D.faces_end()) = bool(plane);
  }