}

  @Override
  public Set<N> successors(N node) {
    return nodeInvalidatableSet(checkedConnections(node).successors(), node);
  }

  @Override
  public Set<EndpointPair<N>> incidentEdges(N node) {
    GraphConnections<N, V> connections = checkedConnections(node);
    IncidentEdgeSet<N> incident =
        new IncidentEdgeSet<N>(this, node) {
          @Override

   */
  @Override
  Set<EndpointPair<N>> incidentEdges(N node);

  /**
   * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently,
   * the number of times an edge touches {@code node}).
   *
   * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of

   */
  @Override
  Set<EndpointPair<N>> incidentEdges(N node);

  /**
   * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently,
   * the number of times an edge touches {@code node}).
   *
   * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of

    Function<N, Presence> edgeValueFn =
        (Function<N, Presence>) Functions.constant(Presence.EDGE_EXISTS);
    return graph.isDirected()
        ? DirectedGraphConnections.ofImmutable(node, graph.incidentEdges(node), edgeValueFn)
        : UndirectedGraphConnections.ofImmutable(
            Maps.asMap(graph.adjacentNodes(node), edgeValueFn));
  }

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

            .<Integer, String>immutable()
            .putEdgeValue(2, 1, "2-1")
            .putEdgeValue(2, 3, "2-3")
            .putEdgeValue(1, 2, "1-2")
            .build();

    assertThat(graph.incidentEdges(2))
        .containsExactly(
            EndpointPair.ordered(2, 1), EndpointPair.ordered(2, 3), EndpointPair.ordered(1, 2))
        .inOrder();
  }

  @Test

            requireNonNull(graph.edgeValueOrDefault(node, successorNode, null));
    return graph.isDirected()
        ? DirectedGraphConnections.ofImmutable(
            node, graph.incidentEdges(node), successorNodeToValueFn)
        : UndirectedGraphConnections.ofImmutable(
            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
  }

  /**

    }

    // Since views are returned, we need to copy the edges that will be removed.
    // Thus we avoid modifying the underlying view while iterating over it.
    for (E edge : ImmutableList.copyOf(connections.incidentEdges())) {
      removeEdge(edge);
    }
    nodeConnections.remove(node);
    return true;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeEdge(E edge) {

    graph.putEdgeValue(2, 1, "2-1");
    graph.putEdgeValue(2, 3, "2-3");
    graph.putEdgeValue(1, 2, "1-2");

    assertThat(graph.incidentEdges(2))
        .containsExactly(
            EndpointPair.ordered(2, 1), EndpointPair.ordered(2, 3), EndpointPair.ordered(1, 2))
        .inOrder();
  }

  @Test

      }
    };
  }

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

  @Override
  public Set<EndpointPair<N>> incidentEdges(N node) {
    checkNotNull(node);
    checkArgument(nodes().contains(node), "Node %s is not an element of this graph.", node);
    IncidentEdgeSet<N> incident =
        new IncidentEdgeSet<N>(this, node) {

    graph.putEdgeValue(2, 1, "2-1");
    graph.putEdgeValue(2, 3, "2-3");
    graph.putEdgeValue(1, 2, "1-2");

    assertThat(graph.incidentEdges(2))
        .containsExactly(
            EndpointPair.ordered(2, 1), EndpointPair.ordered(2, 3), EndpointPair.ordered(1, 2))
        .inOrder();
  }

  @Test