return delegate().successors(node);
  }

  @Override
  public Set<E> incidentEdges(N node) {
    return delegate().incidentEdges(node);
  }

  @Override
  public Set<E> inEdges(N node) {
    return delegate().inEdges(node);
  }

  @Override
  public Set<E> outEdges(N node) {
    return delegate().outEdges(node);
  }

  @Override
  public EndpointPair<N> incidentNodes(E edge) {

    return adjacentNodes();
  }

  @Override
  public Set<E> incidentEdges() {
    return Collections.unmodifiableSet(incidentEdgeMap.keySet());
  }

  @Override
  public Set<E> inEdges() {
    return incidentEdges();
  }

  @Override
  public Set<E> outEdges() {
    return incidentEdges();
  }

  @Override
  public N adjacentNode(E edge) {

    return nodePairInvalidatableSet(connectionsU.edgesConnecting(nodeV), nodeU, nodeV);
  }

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

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

  @Override

    return nodePairInvalidatableSet(connectionsU.edgesConnecting(nodeV), nodeU, nodeV);
  }

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

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

  @Override

      }

      @Override
      public boolean contains(@CheckForNull Object obj) {
        return inEdgeMap.containsKey(obj) || outEdgeMap.containsKey(obj);
      }
    };
  }

  @Override
  public Set<E> inEdges() {
    return Collections.unmodifiableSet(inEdgeMap.keySet());
  }

  @Override
  public Set<E> outEdges() {
    return Collections.unmodifiableSet(outEdgeMap.keySet());
  }

  @Override

 */
@ElementTypesAreNonnullByDefault
interface NetworkConnections<N, E> {

  Set<N> adjacentNodes();

  Set<N> predecessors();

  Set<N> successors();

  Set<E> incidentEdges();

  Set<E> inEdges();

  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.
   */

      }

      @Override
      public boolean contains(@CheckForNull Object obj) {
        return inEdgeMap.containsKey(obj) || outEdgeMap.containsKey(obj);
      }
    };
  }

  @Override
  public Set<E> inEdges() {
    return Collections.unmodifiableSet(inEdgeMap.keySet());
  }

  @Override
  public Set<E> outEdges() {
    return Collections.unmodifiableSet(outEdgeMap.keySet());
  }

  @Override

   *         <li>{@code successors(node)}: Connecting edge insertion order
   *         <li>{@code incidentEdges(node)}: Stable order
   *         <li>{@code inEdges(node)}: Edge insertion order
   *         <li>{@code outEdges(node)}: Edge insertion order
   *         <li>{@code adjacentEdges(edge)}: Stable order
   *         <li>{@code edgesConnecting(nodeU, nodeV)}: Edge insertion order

   *         <li>{@code successors(node)}: Connecting edge insertion order
   *         <li>{@code incidentEdges(node)}: Stable order
   *         <li>{@code inEdges(node)}: Edge insertion order
   *         <li>{@code outEdges(node)}: Edge insertion order
   *         <li>{@code adjacentEdges(edge)}: Stable order
   *         <li>{@code edgesConnecting(nodeU, nodeV)}: Edge insertion order