}

  @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.
   */

    assertSame(Ordering.natural(), set.comparator());
  }

  public void testSingle_headSet() {
    SortedSet<String> set = of("e");
    assertTrue(set.headSet("g") instanceof ImmutableSortedSet);
    assertThat(set.headSet("g")).contains("e");
    assertSame(this.<String>of(), set.headSet("c"));
    assertSame(this.<String>of(), set.headSet("e"));
  }

  public void testSingle_tailSet() {
    SortedSet<String> set = of("e");

    NavigableSet<String> set = create();
    SortedSet<String> headSet = set.headSet("a");
    assertTrue(headSet instanceof SynchronizedSortedSet);
    assertSame(set, ((SynchronizedSortedSet<String>) headSet).mutex);
  }

  public void testHeadSet_E_B() {
    NavigableSet<String> set = create();
    NavigableSet<String> headSet = set.headSet("a", true);
    assertTrue(headSet instanceof SynchronizedNavigableSet);

    NavigableSet<String> map = create();
    SortedSet<String> headSet = map.headSet("a");
    assertTrue(headSet instanceof SynchronizedSortedSet);
    assertSame(MUTEX, ((SynchronizedSortedSet<String>) headSet).mutex);
  }

  public void testHeadSet_E_B() {
    NavigableSet<String> map = create();
    NavigableSet<String> headSet = map.headSet("a", true);
    assertTrue(headSet instanceof SynchronizedNavigableSet);

    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();

    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();

  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) {

    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

  }

  @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.
   */

  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) {