}
  }

  /** A skeleton navigable implementation for {@link SortedMultiset#elementSet}. */
  @GwtIncompatible // Navigable
  static class NavigableElementSet<E extends @Nullable Object> extends ElementSet<E>
      implements NavigableSet<E> {
    NavigableElementSet(SortedMultiset<E> multiset) {
      super(multiset);
    }

    @Override
    public @Nullable E lower(@ParametricNullness E e) {

  }

  @Override
  public NavigableSet<E> elementSet() {
    return (NavigableSet<E>) super.elementSet();
  }

  @Override
  NavigableSet<E> createElementSet() {
    return new SortedMultisets.NavigableElementSet<>(this);
  }

  @Override
  public Comparator<? super E> comparator() {
    return comparator;
  }

  @Override
  public @Nullable Entry<E> firstEntry() {

   * implementation or a subclass thereof.
   *
   * @since 15.0
   */
  protected class StandardElementSet extends SortedMultisets.NavigableElementSet<E> {
    /** Constructor for use by subclasses. */
    public StandardElementSet() {
      super(ForwardingSortedMultiset.this);
    }
  }

  @Override
  public Comparator<? super E> comparator() {

   * implementation or a subclass thereof.
   *
   * @since 15.0
   */
  protected class StandardElementSet extends SortedMultisets.NavigableElementSet<E> {
    /** Constructor for use by subclasses. */
    public StandardElementSet() {
      super(ForwardingSortedMultiset.this);
    }
  }

  @Override
  public Comparator<? super E> comparator() {