function append ($list)
  {
    $cur = $this->getIterator ();
    if ($cur instanceof AppendIterator) {
      foreach (iterator ($list) as $it)
        $cur->append (iterator ($it));
    }
    else {
      $a = new AppendIterator;
      $a->append ($cur);
      foreach (iterator ($list) as $it)
        $a->append (iterator ($it));
      $this->setIterator ($a);
    }
    return $this;
  }