return subSetImpl(fromElement, fromInclusive, toElement, toInclusive);
  }

  @Override
  public ContiguousSet<C> tailSet(C fromElement) {
    return tailSetImpl(checkNotNull(fromElement), true);
  }

  /** @since 12.0 */
  @GwtIncompatible // NavigableSet
  @Override
  public ContiguousSet<C> tailSet(C fromElement, boolean inclusive) {
    return tailSetImpl(checkNotNull(fromElement), inclusive);
  }

  /*

    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return multiset().headMultiset(toElement, OPEN).elementSet();
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
      return multiset().tailMultiset(fromElement, CLOSED).elementSet();
    }

    @Override
    @ParametricNullness
    public E first() {

    return subSetImpl(fromElement, fromInclusive, toElement, toInclusive);
  }

  @Override
  public ContiguousSet<C> tailSet(C fromElement) {
    return tailSetImpl(checkNotNull(fromElement), true);
  }

  /** @since 12.0 */
  @GwtIncompatible // NavigableSet
  @Override
  public ContiguousSet<C> tailSet(C fromElement, boolean inclusive) {
    return tailSetImpl(checkNotNull(fromElement), inclusive);
  }

  /*

          sortedMap().subMap(fromElement, fromInclusive, toElement, toInclusive));
    }

    @Override
    public NavigableSet<K> tailSet(@ParametricNullness K fromElement) {
      return tailSet(fromElement, true);
    }

    @Override
    public NavigableSet<K> tailSet(@ParametricNullness K fromElement, boolean inclusive) {
      return new NavigableKeySet(sortedMap().tailMap(fromElement, inclusive));
    }
  }

      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).tailSet(fromElement), predicate);
    }

    @Override
    @ParametricNullness
    public E first() {

      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).tailSet(fromElement), predicate);
    }

    @Override
    @ParametricNullness
    public E first() {

  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return forward.descendingIterator();
  }

  @Override
  ImmutableSortedSet<E> headSetImpl(E toElement, boolean inclusive) {
    return forward.tailSet(toElement, inclusive).descendingSet();
  }

  @Override
  ImmutableSortedSet<E> subSetImpl(
      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {

          sortedMap().subMap(fromElement, fromInclusive, toElement, toInclusive));
    }

    @Override
    public NavigableSet<K> tailSet(@ParametricNullness K fromElement) {
      return tailSet(fromElement, true);
    }

    @Override
    public NavigableSet<K> tailSet(@ParametricNullness K fromElement, boolean inclusive) {
      return new NavigableKeySet(sortedMap().tailMap(fromElement, inclusive));
    }
  }

  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return forward.descendingIterator();
  }

  @Override
  ImmutableSortedSet<E> headSetImpl(E toElement, boolean inclusive) {
    return forward.tailSet(toElement, inclusive).descendingSet();
  }

  @Override
  ImmutableSortedSet<E> subSetImpl(
      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {

   *
   * <p>The {@link SortedSet#tailSet} documentation states that a subset of a subset throws an
   * {@link IllegalArgumentException} if passed a {@code fromElement} smaller than an earlier {@code
   * fromElement}. However, this method doesn't throw an exception in that situation, but instead
   * keeps the original {@code fromElement}.
   */
  @Override
  public ImmutableSortedSet<E> tailSet(E fromElement) {