* }</pre>
   *
   * <p>This is unfortunate, but should come up only very rarely.
   */
  public static <E extends @Nullable Object> SetView<E> intersection(
      final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {