@ParametricNullness
      E transform(Entry<E> entry) {
        return entry.getElement();
      }
    };
  }

  abstract static class ElementSet<E extends @Nullable Object> extends Sets.ImprovedAbstractSet<E> {
    abstract Multiset<E> multiset();

    @Override
    public void clear() {
      multiset().clear();
    }

    @Override
    public boolean contains(@Nullable Object o) {

      @ParametricNullness
      E transform(Entry<E> entry) {
        return entry.getElement();
      }
    };
  }

  abstract static class ElementSet<E extends @Nullable Object> extends Sets.ImprovedAbstractSet<E> {
    abstract Multiset<E> multiset();

    @Override
    public void clear() {
      multiset().clear();
    }

    @Override
    public boolean contains(@Nullable Object o) {

        return new ValueForKeyIterator(key, index);
      }
    };
  }

  @Override
  Set<K> createKeySet() {
    @WeakOuter
    final class KeySetImpl extends Sets.ImprovedAbstractSet<K> {
      @Override
      public int size() {
        return keyToKeyList.size();
      }

      @Override
      public Iterator<K> iterator() {
        return new DistinctKeyIterator();