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

  /**

    switch (strategy) {
      case ADD_SELF_LOOPS_ALWAYS: // always include 'node'
        return traverser.breadthFirst(node);
      case ADD_SELF_LOOPS_FOR_CYCLES: // include 'node' iff there's an incident cycle
        // note that if 'node' has a self-loop, it will appear in its successors
        return traverser.breadthFirst(graph.successors(node));
    }
    throw new IllegalArgumentException("Unrecognized strategy: " + strategy);
  }