}

    @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();