}

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

  @Override
  public Set<E> edgesConnecting(N node) {
    return new EdgesConnecting<>(((BiMap<E, N>) incidentEdgeMap).inverse(), node);
  }

    assertThat(directedGraph.edges()).isEmpty();
    assertThat(directedGraph.addEdge(N1, N2, E12)).isTrue();
    assertThat(directedGraph.edgesConnecting(N1, N2)).isEqualTo(ImmutableSet.of(E12));
    assertThat(directedGraph.edgesConnecting(N2, N1)).isEmpty();

    // By default, parallel edges are not allowed.
    IllegalArgumentException e =

  public int outDegree(N node) {
    return delegate().outDegree(node);
  }

  @Override
  public Set<E> edgesConnecting(N nodeU, N nodeV) {
    return delegate().edgesConnecting(nodeU, nodeV);
  }

  @Override
  public Set<E> edgesConnecting(EndpointPair<N> endpoints) {
    return delegate().edgesConnecting(endpoints);
  }

  @Override
  public @Nullable E edgeConnectingOrNull(N nodeU, N nodeV) {

  }

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

  @Override
  public Set<E> edgesConnecting(N node) {
    return new EdgesConnecting<>(((BiMap<E, N>) outEdgeMap).inverse(), node);
  }

  }

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

  @Override
  public Set<E> edgesConnecting(N node) {
    return new EdgesConnecting<>(((BiMap<E, N>) outEdgeMap).inverse(), node);
  }

      adjacentNodes = HashMultiset.create(incidentEdgeMap.values());
      adjacentNodesReference = new SoftReference<>(adjacentNodes);
    }
    return adjacentNodes;
  }

  @Override
  public Set<E> edgesConnecting(N node) {
    return new MultiEdgesConnecting<E>(incidentEdgeMap, node) {
      @Override
      public int size() {
        return adjacentNodesMultiset().count(node);
      }
    };
  }

  @Override

    }

    @Override
    public Set<E> edgesConnecting(N nodeU, N nodeV) {
      return delegate().edgesConnecting(nodeV, nodeU); // transpose
    }

    @Override
    public Set<E> edgesConnecting(EndpointPair<N> endpoints) {
      return delegate().edgesConnecting(transpose(endpoints));
    }

    @Override

  Set<E> outEdges();

  /**
   * Returns the set of edges connecting the origin node to {@code node}. For networks without
   * parallel edges, this set cannot be of size greater than one.
   */
  Set<E> edgesConnecting(N node);

  /**
   * Returns the node that is adjacent to the origin node along {@code edge}.
   *
   * <p>In the directed case, {@code edge} is assumed to be an outgoing edge.
   */
  N adjacentNode(E edge);

      successors = HashMultiset.create(outEdgeMap.values());
      successorsReference = new SoftReference<>(successors);
    }
    return successors;
  }

  @Override
  public Set<E> edgesConnecting(N node) {
    return new MultiEdgesConnecting<E>(outEdgeMap, node) {
      @Override
      public int size() {
        return successorsMultiset().count(node);
      }
    };
  }

  @Override

      successors = HashMultiset.create(outEdgeMap.values());
      successorsReference = new SoftReference<>(successors);
    }
    return successors;
  }

  @Override
  public Set<E> edgesConnecting(N node) {
    return new MultiEdgesConnecting<E>(outEdgeMap, node) {
      @Override
      public int size() {
        return successorsMultiset().count(node);
      }
    };
  }

  @Override