@Override
    public String toString() {
      int h = 0, t = 0;
      for (P2<T> p = prev; p != null; p = p.prev) h++;
      for (P2<T> p = next; p != null; p = p.next) t++;
      return h + " of " + (h + t + 1) + ": " + node;
    }
@Override
    public String toString()