*/
  Set<N> adjacentNodes(N node);

  /**
   * Returns a live view of all nodes in this network adjacent to {@code node} which can be reached
   * by traversing {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge.
   *
   * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}.
   *