super(Ordering.natural());
    this.domain = domain;
  }

  @Override
  public ContiguousSet<C> headSet(C toElement) {
    return headSetImpl(checkNotNull(toElement), false);
  }

  /**
   * @since 12.0
   */
  @GwtIncompatible // NavigableSet
  @Override
  public ContiguousSet<C> headSet(C toElement, boolean inclusive) {
    return headSetImpl(checkNotNull(toElement), inclusive);
  }

    public Iterator<K> descendingIterator() {
      return descendingSet().iterator();
    }

    @Override
    public NavigableSet<K> headSet(@ParametricNullness K toElement) {
      return headSet(toElement, false);
    }

    @Override
    public NavigableSet<K> headSet(@ParametricNullness K toElement, boolean inclusive) {
      return new NavigableKeySet(sortedMap().headMap(toElement, inclusive));
    }

   *
   * <p>The {@link SortedSet#headSet} documentation states that a subset of a subset throws an
   * {@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) {

    assertThat(set.headSet(1)).isEmpty();
    assertThat(set.headSet(2)).containsExactly(1).inOrder();
    assertThat(set.headSet(3)).containsExactly(1, 2).inOrder();
    assertThat(set.headSet(4)).containsExactly(1, 2, 3).inOrder();
    assertThat(set.headSet(Integer.MAX_VALUE)).containsExactly(1, 2, 3).inOrder();
    assertThat(set.headSet(1, true)).containsExactly(1).inOrder();

          ((SortedSet<E>) unfiltered).subSet(fromElement, toElement), predicate);
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {

   *
   * <p>The {@link SortedSet#headSet} documentation states that a subset of a subset throws an
   * {@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) {

    public Iterator<K> descendingIterator() {
      return descendingSet().iterator();
    }

    @Override
    public NavigableSet<K> headSet(@ParametricNullness K toElement) {
      return headSet(toElement, false);
    }

    @Override
    public NavigableSet<K> headSet(@ParametricNullness K toElement, boolean inclusive) {
      return new NavigableKeySet(sortedMap().headMap(toElement, inclusive));
    }

          ((SortedSet<E>) unfiltered).subSet(fromElement, toElement), predicate);
    }

    @Override
    public SortedSet<E> headSet(@ParametricNullness E toElement) {
      return new FilteredSortedSet<>(((SortedSet<E>) unfiltered).headSet(toElement), predicate);
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {

    assertThat(set.headSet(1)).isEmpty();
    assertThat(set.headSet(2)).containsExactly(1).inOrder();
    assertThat(set.headSet(3)).containsExactly(1, 2).inOrder();
    assertThat(set.headSet(4)).containsExactly(1, 2, 3).inOrder();
    assertThat(set.headSet(Integer.MAX_VALUE)).containsExactly(1, 2, 3).inOrder();
    assertThat(set.headSet(1, true)).containsExactly(1).inOrder();

    SortedSet<String> set = of("e", "f", "b", "d", "c");
    assertTrue(set.headSet("e") instanceof ImmutableSortedSet);
    assertThat(set.headSet("e")).containsExactly("b", "c", "d").inOrder();
    assertThat(set.headSet("g")).containsExactly("b", "c", "d", "e", "f").inOrder();
    assertThat(set.headSet("a")).isSameInstanceAs(this.<String>of());
    assertThat(set.headSet("b")).isSameInstanceAs(this.<String>of());
  }