    operator()(Halfedge_handle e, const Tag_true& ) const
    {
      return D_.face(e)==f_ || D_.face(D_.twin(e))==f_;
    }
    operator()(Halfedge_handle e, const Tag_true& ) const
    {
      return D_.face(e)==f_ || D_.face(D_.twin(e))==f_;
    }