}

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

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

    @Override
    public @Nullable E pollFirst() {

    }

    @LazyInit private transient @Nullable 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();

    @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();

  transient @Nullable ImmutableSortedSet<E> descendingSet;

  /**
   * @since 12.0
   */
  @GwtIncompatible // NavigableSet
  @Override
  public ImmutableSortedSet<E> descendingSet() {
    // racy single-check idiom
    ImmutableSortedSet<E> result = descendingSet;
    if (result == null) {
      result = descendingSet = createDescendingSet();
      result.descendingSet = this;
    }
    return result;
  }

      return new WrappedNavigableSet(key, wrapped, (getAncestor() == null) ? this : getAncestor());
    }

    @Override
    public NavigableSet<V> descendingSet() {
      return wrap(getSortedSetDelegate().descendingSet());
    }

    @Override
    public Iterator<V> descendingIterator() {
      return new WrappedIterator(getSortedSetDelegate().descendingIterator());
    }

    @Override

    /* Unmodifiable is a view. */
    mod.add(4);
    assertTrue(unmod.contains(4));
    assertTrue(unmod.descendingSet().contains(4));

    ensureNotDirectlyModifiable(unmod);
    ensureNotDirectlyModifiable(unmod.descendingSet());
    ensureNotDirectlyModifiable(unmod.headSet(2));
    ensureNotDirectlyModifiable(unmod.headSet(2, true));

              .createTestSuite());

      suite.addTest(
          NavigableSetTestSuiteBuilder.using(new ContiguousSetDescendingGenerator())
              .named("Range.asSet.descendingSet")
              .withFeatures(
                  CollectionSize.ANY,
                  KNOWN_ORDER,
                  ALLOWS_NULL_QUERIES,
                  NON_STANDARD_TOSTRING,

              .createTestSuite());

      suite.addTest(
          NavigableSetTestSuiteBuilder.using(new ContiguousSetDescendingGenerator())
              .named("Range.asSet.descendingSet")
              .withFeatures(
                  CollectionSize.ANY,
                  KNOWN_ORDER,
                  ALLOWS_NULL_QUERIES,
                  NON_STANDARD_TOSTRING,

            .createTestSuite());

    suite.addTest(
        ListTestSuiteBuilder.using(new ImmutableSortedSetDescendingAsListGenerator())
            .named("ImmutableSortedSet.descendingSet.asList")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.REJECTS_DUPLICATES_AT_CREATION,
                CollectionFeature.SERIALIZABLE,