@GwtIncompatible("NavigableSet")
  public UnmodifiableIterator<E> descendingIterator() {
    return forward.iterator();
  }

  @Override
  @GwtIncompatible("NavigableSet")
  ImmutableSortedSet<E> createDescendingSet() {
    throw new AssertionError("should never be called");
  }

  @Override
  public @Nullable E lower(E element) {
    return forward.higher(element);
  }

  @Override

    throw new InvalidObjectException("Use SerializedForm");
  }

  @GwtIncompatible // NavigableSet
  @Override
  ImmutableSortedSet<C> createDescendingSet() {
    return ImmutableSortedSet.emptySet(Ordering.<C>natural().reverse());
  }

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

  // Most classes should implement this as new DescendingImmutableSortedSet<E>(this),

          }
        }
        throw new AssertionError("impossible");
      }
      return -1;
    }

    @Override
    ImmutableSortedSet<C> createDescendingSet() {
      return new DescendingImmutableSortedSet<>(this);
    }

    @Override
    boolean isPartialView() {
      return ranges.isPartialView();
    }

    @Override