* of a subclass of {@code StandardDescendingMultiset}.
   *
   * @since 15.0
   */
  protected abstract class StandardDescendingMultiset extends DescendingMultiset<E> {
    /** Constructor for use by subclasses. */
    public StandardDescendingMultiset() {}

    @Override
    SortedMultiset<E> forwardMultiset() {

   * of a subclass of {@code StandardDescendingMultiset}.
   *
   * @since 15.0
   */
  protected abstract class StandardDescendingMultiset extends DescendingMultiset<E> {
    /** Constructor for use by subclasses. */
    public StandardDescendingMultiset() {}

    @Override
    SortedMultiset<E> forwardMultiset() {