transient @Nullable NavigableSet<E> descendingSet;

    @Override
    public NavigableSet<E> descendingSet() {
      synchronized (mutex) {
        if (descendingSet == null) {
          NavigableSet<E> dS = Synchronized.navigableSet(delegate().descendingSet(), mutex);
          descendingSet = dS;
          return dS;
        }
        return descendingSet;
      }
    }

    @Override

              @Override
              public Set<E> create(Object... elements) {
                NavigableSet<E> navigableSet = (NavigableSet<E>) delegate.create(elements);
                return navigableSet.descendingSet();
              }
            })
        .named(parentBuilder.getName() + " descending")
        .withFeatures(features)
        .suppressing(parentBuilder.getSuppressedTests())
        .createTestSuite();

      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

    NavigableSet<E> empty = navigableSet.subSet(e0(), false, e0(), false);
    assertEquals(new TreeSet<E>(), empty);
  }

  /*
   * TODO(cpovirk): more testing of subSet/headSet/tailSet/descendingSet? and/or generate derived
   * suites?
   */

  /**
   * Returns the {@link Method} instances for the test methods in this class that create a set with

    NavigableSet<E> empty = navigableSet.subSet(e0(), false, e0(), false);
    assertEquals(new TreeSet<E>(), empty);
  }

  /*
   * TODO(cpovirk): more testing of subSet/headSet/tailSet/descendingSet? and/or generate derived
   * suites?
   */

  /**
   * Returns the {@link Method} instances for the test methods in this class that create a set with

              .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,

        return removeOnlyNavigableSet(super.tailSet(fromElement, inclusive));
      }

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

  /**
   * Returns an immutable map whose keys are the distinct elements of {@code keys} and whose value

        return removeOnlyNavigableSet(super.tailSet(fromElement, inclusive));
      }

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

  /**
   * Returns an immutable map whose keys are the distinct elements of {@code keys} and whose value

            (RegularImmutableSortedSet<K>) keySet.descendingSet(), valueList.reverse(), this);
      }
    }
    return result;
  }

  @Override
  public ImmutableSortedSet<K> navigableKeySet() {
    return keySet;
  }

  @Override
  public ImmutableSortedSet<K> descendingKeySet() {
    return keySet.descendingSet();
  }

  /**