* to forward to this implementation.
   *
   * @since 7.0
   */
  @Override
  protected boolean standardRemoveAll(Collection<?> elementsToRemove) {
    return Multisets.removeAllImpl(this, elementsToRemove);
  }

  /**
   * A sensible definition of {@link #retainAll} in terms of the {@code retainAll} method of {@link

        /*
         * We can't inherit the normal implementation (which calls
         * Sets.removeAllImpl(Set, *Collection*)) because, under some
         * circumstances, it attempts to call columnKeySet().iterator().remove,
         * which is unsupported.
         */
        checkNotNull(c);
        return Sets.removeAllImpl(this, c.iterator());
      }

      @Override
      public boolean retainAll(Collection<?> c) {

  }

  /** Remove each element in an iterable from a set. */
  static boolean removeAllImpl(Set<?> set, Iterator<?> iterator) {
    boolean changed = false;
    while (iterator.hasNext()) {
      changed |= set.remove(iterator.next());
    }
    return changed;
  }

  static boolean removeAllImpl(Set<?> set, Collection<?> collection) {
    checkNotNull(collection); // for GWT

      // Guava issue 1013: AbstractSet and most JDK set implementations are
      // susceptible to quadratic removeAll performance on lists;
      // use a slightly smarter implementation here
      boolean changed = Sets.removeAllImpl((Set<V>) delegate, c);
      if (changed) {
        int newSize = delegate.size();
        totalSize += newSize - oldSize;
        removeIfEmpty();
      }
      return changed;
    }
  }