return forward.tailSet(toElement, inclusive).descendingSet();
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return standardHeadSet(toElement);
    }

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

      return forward.tailSet(toElement, inclusive).descendingSet();
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return standardHeadSet(toElement);
    }

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