public boolean removeAll(Collection<?> keysToRemove) {
      return standardRemoveAll(keysToRemove);
    }

    @Override
    public boolean retainAll(Collection<?> keysToRetain) {
      return standardRetainAll(keysToRetain);
    }

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

  @LazyInit private transient @Nullable Set<V> valueSet;

   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #retainAll}
   * to forward to this implementation.
   *
   * @since 7.0
   */
  @Override
  protected boolean standardRetainAll(Collection<?> elementsToRetain) {
    return Multisets.retainAllImpl(this, elementsToRetain);
  }

  /**
   * A sensible definition of {@link #setCount(Object, int)} in terms of {@link #count(Object)},

    @Override
    public boolean removeAll(Collection<?> collection) {
      return standardRemoveAll(collection);
    }

    @Override
    public boolean retainAll(Collection<?> collection) {
      return standardRetainAll(collection);
    }

    @Override
    public Object[] toArray() {
      return standardToArray();
    }

    @Override
    public <T> T[] toArray(T[] array) {

   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #retainAll}
   * to forward to this implementation.
   *
   * @since 7.0
   */
  @Override
  protected boolean standardRetainAll(Collection<?> elementsToRetain) {
    return Multisets.retainAllImpl(this, elementsToRetain);
  }

  /**
   * A sensible definition of {@link #setCount(Object, int)} in terms of {@link #count(Object)},