static <V extends @Nullable Object> Function<Entry<?, V>, V> valueFunction() {
    return (Function) EntryFunction.VALUE;
  }

  static <K extends @Nullable Object, V extends @Nullable Object> Iterator<K> keyIterator(
      Iterator<Entry<K, V>> entryIterator) {
    return new TransformedIterator<Entry<K, V>, K>(entryIterator) {
      @Override
      @ParametricNullness
      K transform(Entry<K, V> entry) {

    @Override
    public void remove() {
      checkRemove(lastReturned != null);
      MapMakerInternalMap.this.remove(lastReturned.getKey());
      lastReturned = null;
    }
  }

  final class KeyIterator extends HashIterator<K> {

    @Override
    public K next() {
      return nextEntry().getKey();
    }
  }

  final class ValueIterator extends HashIterator<V> {

    @Override

   * but ProGuard can't figure out how to eliminate that default when RegularImmutableMap
   * overrides it.
   */
  abstract ImmutableSet<K> createKeySet();

  UnmodifiableIterator<K> keyIterator() {
    final UnmodifiableIterator<Entry<K, V>> entryIterator = entrySet().iterator();
    return new UnmodifiableIterator<K>() {
      @Override
      public boolean hasNext() {
        return entryIterator.hasNext();

   * but ProGuard can't figure out how to eliminate that default when RegularImmutableMap
   * overrides it.
   */
  abstract ImmutableSet<K> createKeySet();

  UnmodifiableIterator<K> keyIterator() {
    final UnmodifiableIterator<Entry<K, V>> entryIterator = entrySet().iterator();
    return new UnmodifiableIterator<K>() {
      @Override
      public boolean hasNext() {

    @Override
    public void remove() {
      checkState(lastReturned != null);
      LocalCache.this.remove(lastReturned.getKey());
      lastReturned = null;
    }
  }

  final class KeyIterator extends HashIterator<K> {

    @Override
    public K next() {
      return nextEntry().getKey();
    }
  }

  final class ValueIterator extends HashIterator<V> {

    @Override

    @Override
    public boolean contains(@CheckForNull Object element) {
      return multimap.containsKey(element);
    }

    @Override
    public Iterator<K> iterator() {
      return Maps.keyIterator(multimap.entries().iterator());
    }

    @Override
    public int count(@CheckForNull Object element) {
      Collection<V> values = Maps.safeGet(multimap.asMap(), element);