graph.adjacentNodes(node).iterator(),
                      (N adjacentNode) -> EndpointPair.unordered(node, adjacentNode)));
            }
          }
        };
    return nodeInvalidatableSet(incident, node);
  }

  @Override
  public int degree(N node) {
    if (isDirected()) {
      return IntMath.saturatedAdd(predecessors(node).size(), successors(node).size());
    } else {

  /**
   * Returns a {@link Set} whose methods throw {@link IllegalStateException} when the given node is
   * not present in this network.
   *
   * @since 33.1.0
   */
  protected final <T> Set<T> nodeInvalidatableSet(Set<T> set, N node) {
    return InvalidatableSet.of(
        set, () -> nodes().contains(node), () -> String.format(NODE_REMOVED_FROM_GRAPH, node));
  }

  /**

  /**
   * Returns a {@link Set} whose methods throw {@link IllegalStateException} when the given node is
   * not present in this network.
   *
   * @since 33.1.0
   */
  protected final <T> Set<T> nodeInvalidatableSet(Set<T> set, N node) {
    return InvalidatableSet.of(
        set, () -> nodes().contains(node), () -> String.format(NODE_REMOVED_FROM_GRAPH, node));
  }

  /**