  Nef_polyhedron_2<T,Items,Mark> transform(const Aff_transformation& t) const
  /*{\Mop returns $t(|\Mvar|)$.}*/
  { Nef_polyhedron_2<T,Items,Mark> res(pm()); // cloned
    Transformer PMT(res.pm());
    PMT.transform(t);
    return res;
  }
  Nef_polyhedron_2<T,Items,Mark> transform(const Aff_transformation& t) const
   
  { Nef_polyhedron_2<T,Items,Mark> res(pm());  
    Transformer PMT(res.pm());
    PMT.transform(t);
    return res;
  }