}

  @Override
  public NavigableSet<E> headSet(@ParametricNullness E toElement, boolean inclusive) {
    return delegate().headSet(toElement, inclusive);
  }

  /**
   * A sensible definition of {@link #headSet(Object)} in terms of the {@link #headSet(Object,
   * boolean)} method. If you override {@link #headSet(Object, boolean)}, you may wish to override
   * {@link #headSet(Object)} to forward to this implementation.
   */

    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();

    return delegate().comparator();
  }

  @Override
  @ParametricNullness
  public E first() {
    return delegate().first();
  }

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

  @Override
  @ParametricNullness
  public E last() {
    return delegate().last();
  }

  @Override

    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();
    assertSame(this.<String>of(), set.headSet("a"));
    assertSame(this.<String>of(), set.headSet("b"));
  }

  public void testOf_tailSet() {

    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);
  }

  @Override

  public @Nullable E floor(E e) {
    return delegate.floor(checkValid(e));
  }

  @Override
  public SortedSet<E> headSet(E toElement) {
    return headSet(toElement, false);
  }

  @Override
  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
    return new SafeTreeSet<>(delegate.headSet(checkValid(toElement), inclusive));
  }

  @Override
  public @Nullable E higher(E e) {

      for (List<Integer> contents : SAMPLE_INPUTS) {
        for (int i = 0; i < 10; i++) {
          assertEquals(
              filter((C) createUnfiltered(contents).headSet(i), EVEN),
              filter(createUnfiltered(contents), EVEN).headSet(i));
        }
      }
    }

    @SuppressWarnings("unchecked")
    public void testTailSet() {
      for (List<Integer> contents : SAMPLE_INPUTS) {

    ImmutableSortedSet<E> set = headSet(e, true);
    return !set.isEmpty() ? set.last() : null;
  }

  public ImmutableSortedSet<E> headSet(E toElement, boolean inclusive) {
    checkNotNull(toElement);
    if (inclusive) {
      E tmp = higher(toElement);
      if (tmp == null) {
        return this;
      }
      toElement = tmp;
    }
    return headSet(toElement);
  }

  public E last() {

    ImmutableSortedSet<Integer> asSet = RANGE_SET_ONE.asSet(DiscreteDomain.integers());

    for (int i = 0; i <= 20; i++) {
      assertEquals(asSet.headSet(i, false), expectedSet.headSet(i, false));
      assertEquals(asSet.headSet(i, true), expectedSet.headSet(i, true));
    }
  }

  public void testAsSetTailSet() {
    ImmutableSortedSet<Integer> expectedSet = ImmutableSortedSet.of(2, 3, 4, 8, 9, 16, 17);