@Override
    public @Nullable K ceilingKey(@ParametricNullness K key) {
      return fromMap().ceilingKey(key);
    }

    @Override
    public NavigableSet<K> descendingKeySet() {
      return fromMap().descendingKeySet();
    }

    @Override
    public NavigableMap<K, V2> descendingMap() {
      return transformEntries(fromMap().descendingMap(), transformer);
    }

    @Override

    assertThat(map.headMap("two", false).values()).containsExactly(3, 5).inOrder();
    assertThat(map.headMap("two", false).descendingMap().values()).containsExactly(5, 3).inOrder();
    assertThat(map.descendingKeySet()).containsExactly("two", "three", "one").inOrder();

    assertEquals(mapEntry("one", 3), map.pollFirstEntry());
    assertEquals(mapEntry("two", 3), map.pollLastEntry());
    assertEquals(1, map.size());
  }

      return new NavigableKeySet(sortedMap());
    }

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

    @Override
    public NavigableSet<K> descendingKeySet() {
      return descendingMap().navigableKeySet();
    }

    @Override
    public NavigableMap<K, Collection<V>> subMap(
        @ParametricNullness K fromKey, @ParametricNullness K toKey) {

    assertThat(map.headMap("two", false).values()).containsExactly(3, 5).inOrder();
    assertThat(map.headMap("two", false).descendingMap().values()).containsExactly(5, 3).inOrder();
    assertThat(map.descendingKeySet()).containsExactly("two", "three", "one").inOrder();

    assertEquals(mapEntry("one", 3), map.pollFirstEntry());
    assertEquals(mapEntry("two", 3), map.pollLastEntry());
    assertEquals(1, map.size());
  }

      }
    }
    return result;
  }

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

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

  /**
   * Serialized type for all ImmutableSortedMap instances. It captures the logical contents and they