/** Constructs a {@link MutableGraph} with the properties specified in {@code builder}. */
  StandardMutableGraph(AbstractGraphBuilder<? super N> builder) {
    this.backingValueGraph = new StandardMutableValueGraph<>(builder);
  }

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

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

  /**
   * Returns an empty {@link MutableValueGraph} with the properties of this {@link
   * ValueGraphBuilder}.
   */
  public <N1 extends N, V1 extends V> MutableValueGraph<N1, V1> build() {
    return new StandardMutableValueGraph<>(this);
  }

  ValueGraphBuilder<N, V> copy() {
    ValueGraphBuilder<N, V> newBuilder = new ValueGraphBuilder<>(directed);
    newBuilder.allowsSelfLoops = allowsSelfLoops;