  void visit(SFace_handle h) {
    Done[h]=true;
    if(sf_min == SFace_handle())
      sf_min = h;
    else {
      if(SORT(h,sf_min))
        sf_min = h;
    }
  }
  void visit(SFace_handle h) {
    Done[h]=true;
    if(sf_min == SFace_handle())
      sf_min = h;
    else {
      if(SORT(h,sf_min))
        sf_min = h;
    }
  }