* is in progress or when the iterators generated by {@link #children} are advanced.
   *
   * @deprecated Use {@link com.google.common.graph.Traverser#depthFirstPreOrder} instead, which has
   *     the same behavior.
   */
  @Deprecated
  public final FluentIterable<T> preOrderTraversal(T root) {
    checkNotNull(root);
    return new FluentIterable<T>() {