// (In the backport, we don't need this suppression, but we keep it to minimize diffs.)
  @SuppressWarnings("unchecked")
  @Override
  public UnmodifiableIterator<E> iterator() {
    return (UnmodifiableIterator<E>) Iterators.forArray(elements);
  }

  @Override
  public Spliterator<E> spliterator() {
    return Spliterators.spliterator(elements, SPLITERATOR_CHARACTERISTICS);
  }

      return super.writeReplace();
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }

  @Override
  UnmodifiableIterator<Entry<K, V>> entryIterator() {
    return new UnmodifiableIterator<Entry<K, V>>() {
      final Iterator<? extends Entry<K, ? extends ImmutableCollection<V>>> asMapItr =
          map.entrySet().iterator();
      @Nullable K currentKey = null;

  ImmutableMapKeySet(ImmutableMap<K, V> map) {
    this.map = map;
  }

  @Override
  public int size() {
    return map.size();
  }

  @Override
  public UnmodifiableIterator<K> iterator() {
    return map.keyIterator();
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return map.containsKey(object);
  }

  @Override
  K get(int index) {

  }

  @Override
  int internalArrayEnd() {
    return elements.internalArrayEnd();
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return elements.iterator();
  }

  @GwtIncompatible // NavigableSet
  @Override
  public UnmodifiableIterator<E> descendingIterator() {
    return elements.reverse().iterator();
  }

  @Override
  public Spliterator<E> spliterator() {

  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public boolean contains(@Nullable Object target) {
    return element.equals(target);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return singletonIterator(element);
  }

  @Override
  public ImmutableList<E> asList() {
    return ImmutableList.of(element);
  }

  @Override
  boolean isPartialView() {

      return super.writeReplace();
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }

  @Override
  UnmodifiableIterator<Entry<K, V>> entryIterator() {
    return new UnmodifiableIterator<Entry<K, V>>() {
      final Iterator<? extends Entry<K, ? extends ImmutableCollection<V>>> asMapItr =
          map.entrySet().iterator();
      @Nullable K currentKey = null;

  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public boolean contains(@Nullable Object target) {
    return element.equals(target);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return singletonIterator(element);
  }

  @Override
  public ImmutableList<E> asList() {
    return ImmutableList.of(element);
  }

  @Override
  boolean isPartialView() {

 *       }
 *     };
 * }
 *
 * @author Chris Povirk
 * @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0)
 */
@GwtCompatible
public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
  private @Nullable T nextOrNull;

  /**
   * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
   * creates a new empty iterator.
   */

    @SuppressWarnings("unchecked")
    // requireNonNull is safe because of the contains check.
    C c = (C) requireNonNull(target);
    return (int) domain.distance(first(), c);
  }

  @Override
  public UnmodifiableIterator<C> iterator() {
    return new AbstractSequentialIterator<C>(first()) {
      final C last = last();

      @Override
      protected @Nullable C computeNext(C previous) {

    }

    @Override
    @GwtIncompatible("not used in GWT")
    int copyIntoArray(@Nullable Object[] dst, int offset) {
      return entries.copyIntoArray(dst, offset);
    }

    @Override
    public UnmodifiableIterator<Entry<K, V>> iterator() {
      return entries.iterator();
    }

    @Override
    @GwtIncompatible("Spliterator")
    public Spliterator<Entry<K, V>> spliterator() {