}

    @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

    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

    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

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

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

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

  /**