* Iterables.limit(Traverser.forGraph(graph).depthFirstPreOrder(node), maxNumberOfNodes);
   * }
   *
   * <p>See <a href="https://en.wikipedia.org/wiki/Depth-first_search">Wikipedia</a> for more info.
   *
   * @throws IllegalArgumentException if {@code startNode} is not an element of the graph
   */
  public final Iterable<N> depthFirstPreOrder(N startNode) {
    return depthFirstPreOrder(ImmutableSet.of(startNode));
  }

  /**