// Textbook fragment 06.17
  /** Returns an iterable collection of all the nodes in the list. */
  public Iterable<Position<E>> positions() {     // create a list of posiitons
    PositionList<Position<E>> P = new NodePositionList<Position<E>>();
    if (!isEmpty()) {
      Position<E> p = first();
      while (true) {
        P.addLast(p); // add position p as the last element of list P
        if (p == last())
          break;
        p = next(p);
      }
    }
    return P; // return P as our Iterable object
  }