public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
  //
  // Network-level accessors
  //

  /** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */
  Set<N> nodes();

  /** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */
  Set<E> edges();

  /**