* {@code headSet} and {@code tailSet} methods. In many cases, you may wish to override {@link
   * #subSet(Object, boolean, Object, boolean)} to forward to this implementation.
   */
  protected NavigableSet<E> standardSubSet(
      @ParametricNullness E fromElement,
      boolean fromInclusive,
      @ParametricNullness E toElement,
      boolean toInclusive) {

   * {@code headSet} and {@code tailSet} methods. In many cases, you may wish to override {@link
   * #subSet(Object, boolean, Object, boolean)} to forward to this implementation.
   */
  protected NavigableSet<E> standardSubSet(
      @ParametricNullness E fromElement,
      boolean fromInclusive,
      @ParametricNullness E toElement,
      boolean toInclusive) {

    }

    @Override
    public String toString() {
      return standardToString();
    }

    @Override
    public SortedSet<T> subSet(T fromElement, T toElement) {
      return standardSubSet(fromElement, toElement);
    }
  }

  public static Test suite() {
    TestSuite suite = new TestSuite();

    suite.addTestSuite(ForwardingSortedSetTest.class);
    suite.addTest(

   * {@link #subSet(Object, Object)} to forward to this implementation.
   *
   * @since 7.0
   */
  protected SortedSet<E> standardSubSet(
      @ParametricNullness E fromElement, @ParametricNullness E toElement) {
    return tailSet(fromElement).headSet(toElement);
  }

    }

    @Override
    public String toString() {
      return standardToString();
    }

    @Override
    public SortedSet<T> subSet(T fromElement, T toElement) {
      return standardSubSet(fromElement, toElement);
    }

    @Override
    public @Nullable T lower(T e) {
      return standardLower(e);
    }

    @Override
    public @Nullable T floor(T e) {

   * {@link #subSet(Object, Object)} to forward to this implementation.
   *
   * @since 7.0
   */
  protected SortedSet<E> standardSubSet(
      @ParametricNullness E fromElement, @ParametricNullness E toElement) {
    return tailSet(fromElement).headSet(toElement);
  }

    }

    @Override
    public SortedSet<E> subSet(@ParametricNullness E fromElement, @ParametricNullness E toElement) {
      return standardSubSet(fromElement, toElement);
    }

    @Override
    public NavigableSet<E> headSet(@ParametricNullness E toElement, boolean inclusive) {
      return forward.tailSet(toElement, inclusive).descendingSet();

    }

    @Override
    public SortedSet<E> subSet(@ParametricNullness E fromElement, @ParametricNullness E toElement) {
      return standardSubSet(fromElement, toElement);
    }

    @Override
    public NavigableSet<E> headSet(@ParametricNullness E toElement, boolean inclusive) {
      return forward.tailSet(toElement, inclusive).descendingSet();