@Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override
      public Set<N> nodes() {
        return AbstractNetwork.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {
        if (allowsParallelEdges()) {
          return super.edges(); // Defer to AbstractGraph implementation.
        }

  @Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override
      public Set<N> nodes() {
        return AbstractNetwork.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {
        if (allowsParallelEdges()) {
          return super.edges(); // Defer to AbstractGraph implementation.
        }

    implements ValueGraph<N, V> {
  /** Constructor for use by subclasses. */
  public AbstractValueGraph() {}

  @Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override
      public Set<N> nodes() {
        return AbstractValueGraph.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {

   * <p>A reference implementation of this is provided by {@link AbstractGraph#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**
   * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of
   * the set returned by {@link #edges()}.
   *
   * <p>A reference implementation of this is provided by {@link AbstractGraph#hashCode()}.
   */
  @Override
  int hashCode();

   * <p>A reference implementation of this is provided by {@link AbstractGraph#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**
   * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of
   * the set returned by {@link #edges()}.
   *
   * <p>A reference implementation of this is provided by {@link AbstractGraph#hashCode()}.
   */
  @Override
  int hashCode();