E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
    return forward.subSet(toElement, toInclusive, fromElement, fromInclusive).descendingSet();
  }

  @Override
  ImmutableSortedSet<E> tailSetImpl(E fromElement, boolean inclusive) {
    return forward.headSet(fromElement, inclusive).descendingSet();
  }

  @Override
  @GwtIncompatible("NavigableSet")
  public ImmutableSortedSet<E> descendingSet() {

    return this;
  }

  @Override
  ContiguousSet<C> subSetImpl(
      C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {
    return this;
  }

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean fromInclusive) {
    return this;
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return false;
  }

  @GwtIncompatible // not used by GWT emulation

        Range.range(
            fromElement, BoundType.forBoolean(fromInclusive),
            toElement, BoundType.forBoolean(toInclusive)));
  }

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean inclusive) {
    return intersectionInCurrentDomain(Range.downTo(fromElement, BoundType.forBoolean(inclusive)));
  }

  @GwtIncompatible // not used by GWT emulation
  @Override