@Override
  public NavigableSet<E> descendingSet() {
    return delegate().descendingSet();
  }

  /**
   * A sensible implementation of {@link NavigableSet#descendingSet} in terms of the other methods
   * of {@link NavigableSet}, notably including {@link NavigableSet#descendingIterator}.
   *
   * <p>In many cases, you may wish to override {@link ForwardingNavigableSet#descendingSet} to

    return forward.tailSet(toElement, inclusive).descendingSet();
  }

  @Override
  ImmutableSortedSet<E> subSetImpl(
      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.tailSet(toElement, inclusive).descendingSet();
  }

  @Override
  ImmutableSortedSet<E> subSetImpl(
      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 suite;
  }

  public void testDescendingSet() {
    NavigableSet<String> set = create();
    NavigableSet<String> descendingSet = set.descendingSet();
    assertTrue(descendingSet instanceof SynchronizedNavigableSet);
    assertSame(set, ((SynchronizedNavigableSet<String>) descendingSet).mutex);
  }

  public void testHeadSet_E() {
    NavigableSet<String> set = create();

    return suite;
  }

  public void testDescendingSet() {
    NavigableSet<String> map = create();
    NavigableSet<String> descendingSet = map.descendingSet();
    assertTrue(descendingSet instanceof SynchronizedNavigableSet);
    assertSame(MUTEX, ((SynchronizedNavigableSet<String>) descendingSet).mutex);
  }

  public void testHeadSet_E() {
    NavigableSet<String> map = create();

  @Override
  public NavigableSet<E> descendingSet() {
    return delegate().descendingSet();
  }

  /**
   * A sensible implementation of {@link NavigableSet#descendingSet} in terms of the other methods
   * of {@link NavigableSet}, notably including {@link NavigableSet#descendingIterator}.
   *
   * <p>In many cases, you may wish to override {@link ForwardingNavigableSet#descendingSet} to

    }

    @Override
    public NavigableSet<E> descendingSet() {
      return new NavigableElementSet<>(multiset().descendingMultiset());
    }

    @Override
    public Iterator<E> descendingIterator() {
      return descendingSet().iterator();
    }

    @Override
    @CheckForNull
    public E pollFirst() {

  }

  @Override
  public Iterator<E> descendingIterator() {
    return delegate.descendingIterator();
  }

  @Override
  public NavigableSet<E> descendingSet() {
    return new SafeTreeSet<>(delegate.descendingSet());
  }

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

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

    @LazyInit @CheckForNull private transient UnmodifiableNavigableSet<E> descendingSet;

    @Override
    public NavigableSet<E> descendingSet() {
      UnmodifiableNavigableSet<E> result = descendingSet;
      if (result == null) {
        result = descendingSet = new UnmodifiableNavigableSet<>(delegate.descendingSet());
        result.descendingSet = this;
      }
      return result;
    }

    @Override

    @Override
    protected SortedSet<String> create(String[] elements) {
      return ImmutableSortedSet.<String>reverseOrder().add(elements).build().descendingSet();
    }
  }

  public static class ImmutableSortedSetExplicitComparator extends TestStringSetGenerator {

    private static final Comparator<String> STRING_REVERSED = Collections.reverseOrder();