IncidentEdgeSet<N> incident =
        new IncidentEdgeSet<N>(this, node, IncidentEdgeSet.EdgeType.BOTH) {
          @Override
          public Iterator<EndpointPair<N>> iterator() {
            return connections.incidentEdgeIterator(node);
          }
        };
    return nodeInvalidatableSet(incident, node);
  }

  @Override
  public boolean hasEdgeConnecting(N nodeU, N nodeV) {