abstract class MultiEdgesConnecting<E> extends AbstractSet<E> {

  private final Map<E, ?> outEdgeToNode;
  private final Object targetNode;

  MultiEdgesConnecting(Map<E, ?> outEdgeToNode, Object targetNode) {
    this.outEdgeToNode = checkNotNull(outEdgeToNode);
    this.targetNode = checkNotNull(targetNode);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {