return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<N> incidentEdgeOrder() {
    return delegate().incidentEdgeOrder();
  }

  @Override
  public Set<N> adjacentNodes(N node) {
    return delegate().adjacentNodes(node);
  }

  @Override
  public Set<N> predecessors(N node) {
    return delegate().predecessors(node);
  }

  @Override
  public Set<N> successors(N node) {

  @Test
  public void adjacentNodes_checkReturnedSetMutability() {
    addNode(N1);
    Set<Integer> adjacentNodes = network.adjacentNodes(N1);
    assertThrows(UnsupportedOperationException.class, () -> adjacentNodes.add(N2));
    addEdge(N1, N2, E12);
    assertThat(network.adjacentNodes(N1)).containsExactlyElementsIn(adjacentNodes);
  }

  @Override
  public void adjacentEdges_checkReturnedSetMutability() {
    addEdge(N1, N2, E12);

  public int size() {
    if (graph.isDirected()) {
      return graph.inDegree(node)
          + graph.outDegree(node)
          - (graph.successors(node).contains(node) ? 1 : 0);
    } else {
      return graph.adjacentNodes(node).size();
    }
  }

  @Override
  public boolean contains(@CheckForNull Object obj) {
    if (!(obj instanceof EndpointPair)) {
      return false;
    }

    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<N> incidentEdgeOrder() {
    return delegate().incidentEdgeOrder();
  }

  @Override
  public Set<N> adjacentNodes(N node) {
    return delegate().adjacentNodes(node);
  }

  @Override
  public Set<N> predecessors(N node) {
    return delegate().predecessors(node);
  }

  @Override
  public Set<N> successors(N node) {

    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<N> incidentEdgeOrder() {
    return delegate().incidentEdgeOrder();
  }

  @Override
  public Set<N> adjacentNodes(N node) {
    return delegate().adjacentNodes(node);
  }

  @Override
  public Set<N> predecessors(N node) {
    return delegate().predecessors(node);
  }

  @Override
  public Set<N> successors(N node) {

  }

  @Override
  public Set<N> adjacentNodes() {
    return Collections.unmodifiableSet(adjacentNodeValues.keySet());
  }

  @Override
  public Set<N> predecessors() {
    return adjacentNodes();
  }

  @Override
  public Set<N> successors() {
    return adjacentNodes();
  }

  @Override
  public Iterator<EndpointPair<N>> incidentEdgeIterator(N thisNode) {

      @Override
      public ElementOrder<N> incidentEdgeOrder() {
        return AbstractValueGraph.this.incidentEdgeOrder();
      }

      @Override
      public Set<N> adjacentNodes(N node) {
        return AbstractValueGraph.this.adjacentNodes(node);
      }

      @Override
      public Set<N> predecessors(N node) {
        return AbstractValueGraph.this.predecessors(node);
      }

      @Override

    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<E> edgeOrder() {
    return delegate().edgeOrder();
  }

  @Override
  public Set<N> adjacentNodes(N node) {
    return delegate().adjacentNodes(node);
  }

  @Override
  public Set<N> predecessors(N node) {
    return delegate().predecessors(node);
  }

  @Override
  public Set<N> successors(N node) {

  public int size() {
    if (graph.isDirected()) {
      return graph.inDegree(node)
          + graph.outDegree(node)
          - (graph.successors(node).contains(node) ? 1 : 0);
    } else {
      return graph.adjacentNodes(node).size();
    }
  }

  @Override
  public boolean contains(@CheckForNull Object obj) {
    if (!(obj instanceof EndpointPair)) {
      return false;
    }

  }

  static <N, E> UndirectedNetworkConnections<N, E> ofImmutable(Map<E, N> incidentEdges) {
    return new UndirectedNetworkConnections<>(ImmutableBiMap.copyOf(incidentEdges));
  }

  @Override
  public Set<N> adjacentNodes() {
    return Collections.unmodifiableSet(((BiMap<E, N>) incidentEdgeMap).values());
  }

  @Override
  public Set<E> edgesConnecting(N node) {