{
  void list(int depth, PrintStream out, boolean listNext)  {    for (int i = 0; i < depth; i++)      {        out.print("  ");      }    out.println(toString());    if (children != null)      {        children.list(depth + 1, out, true);      }    if (listNext && next != null)      {        next.list(depth, out, listNext);      }  }