* {@link IllegalArgumentException} if passed a {@code toElement} greater than an earlier {@code
   * toElement}. However, this method doesn't throw an exception in that situation, but instead
   * keeps the original {@code toElement}.
   */
  @Override
  public ImmutableSortedSet<E> headSet(E toElement) {
    return headSet(toElement, false);
  }

  /**
   * @since 12.0
   */
  @Override

    return subSet(fromElement, true, toElement, false);
  }

  ImmutableSortedSet<E> subSet(
      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
    checkNotNull(fromElement);
    checkNotNull(toElement);
    int cmp = comparator().compare(fromElement, toElement);
    checkArgument(cmp <= 0, "fromElement (%s) is less than toElement (%s)", fromElement, toElement);

        boolean fromInclusive,
        @ParametricNullness V toElement,
        boolean toInclusive) {
      return wrap(
          getSortedSetDelegate().subSet(fromElement, fromInclusive, toElement, toInclusive));
    }

    @Override
    public NavigableSet<V> headSet(@ParametricNullness V toElement, boolean inclusive) {
      return wrap(getSortedSetDelegate().headSet(toElement, inclusive));
    }

    @Override

    @Override
    ImmutableSortedSet<C> headSetImpl(C toElement, boolean inclusive) {
      return subSet(Range.upTo(toElement, BoundType.forBoolean(inclusive)));
    }

    @Override
    ImmutableSortedSet<C> subSetImpl(
        C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {
      if (!fromInclusive && !toInclusive && Range.compareOrThrow(fromElement, toElement) == 0) {
        return ImmutableSortedSet.of();