* <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the network was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds {@code edge} connecting {@code nodeU} to {@code nodeV}.
   *
   * <p>If the graph is directed, {@code edge} will be directed in this graph; otherwise, it will be
   * undirected.
   *

        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)
        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)
        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)
        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

    this.backingValueGraph = new StandardMutableValueGraph<>(builder);
  }

  @Override
  BaseGraph<N> delegate() {
    return backingValueGraph;
  }

  @Override
  public boolean addNode(N node) {
    return backingValueGraph.addNode(node);
  }

  @Override
  public boolean putEdge(N nodeU, N nodeV) {
    return backingValueGraph.putEdgeValue(nodeU, nodeV, Presence.EDGE_EXISTS) == null;
  }

  @Override

      default:
        throw new IllegalStateException("Unexpected edge type: " + edgeType);
    }
  }

  @Test
  public void equivalent_nodeSetsDiffer() {
    network.addNode(N1);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    g2.addNode(N2);

    assertThat(network).isNotEqualTo(g2);
  }

  // Node sets are the same, but edge sets differ.
  @Test
  public void equivalent_edgeSetsDiffer() {

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();
      AbstractNetworkTest.validateNetwork(network);

      while (network.nodes().size() < NUM_NODES) {
        network.addNode(gen.nextInt(NODE_POOL_SIZE));
      }
      ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.

        (nodes instanceof Collection)
            ? GraphBuilder.from(graph).expectedNodeCount(((Collection) nodes).size()).build()
            : GraphBuilder.from(graph).build();
    for (N node : nodes) {
      subgraph.addNode(node);
    }
    for (N node : subgraph.nodes()) {
      for (N successorNode : graph.successors(node)) {
        if (subgraph.nodes().contains(successorNode)) {
          subgraph.putEdge(node, successorNode);

      assertThat(graph.nodes()).isEmpty();
      assertThat(graph.edges()).isEmpty();
      AbstractGraphTest.validateGraph(graph);

      while (graph.nodes().size() < NUM_NODES) {
        graph.addNode(gen.nextInt(NODE_POOL_SIZE));
      }
      ArrayList<Integer> nodeList = new ArrayList<>(graph.nodes());
      while (graph.edges().size() < NUM_EDGES) {

      default:
        throw new IllegalStateException("Unexpected edge type: " + edgeType);
    }
  }

  @Test
  public void equivalent_nodeSetsDiffer() {
    graph.addNode(N1);

    MutableGraph<Integer> g2 = createGraph(edgeType);
    g2.addNode(N2);

    assertThat(graph).isNotEqualTo(g2);
  }

  // Node/edge sets are the same, but node/edge connections differ due to edge type.
  @Test