@Override
  public ImmutableSortedMap<K, V> descendingMap() {
    // TODO(kevinb): The descendingMap is never actually cached at all. Either:
    //
    // - Cache it, and annotate the field with @LazyInit.
    // - Simplify the code below, and consider eliminating the field (b/287198172), which is also
    //   set by one of the constructors.
    ImmutableSortedMap<K, V> result = descendingMap;
    if (result == null) {

      }
    }

    transient @Nullable NavigableMap<K, V> descendingMap;

    @Override
    public NavigableMap<K, V> descendingMap() {
      synchronized (mutex) {
        if (descendingMap == null) {
          return descendingMap = navigableMap(delegate().descendingMap(), mutex);
        }
        return descendingMap;
      }
    }

    @Override

      }
    }

    transient @Nullable NavigableMap<K, V> descendingMap;

    @Override
    public NavigableMap<K, V> descendingMap() {
      synchronized (mutex) {
        if (descendingMap == null) {
          return descendingMap = navigableMap(delegate().descendingMap(), mutex);
        }
        return descendingMap;
      }
    }

    @Override

  @Override
  public ImmutableSortedMap<K, V> descendingMap() {
    // TODO(kevinb): The descendingMap is never actually cached at all. Either:
    //
    // - Cache it, and annotate the field with @LazyInit.
    // - Simplify the code below, and consider eliminating the field (b/287198172), which is also
    //   set by one of the constructors.
    ImmutableSortedMap<K, V> result = descendingMap;
    if (result == null) {

    assertThat(map.floorKey("three")).isEqualTo("three");

    assertThat(map.descendingMap().entrySet())
        .containsExactly(mapEntry("two", 3), mapEntry("three", 5), mapEntry("one", 3))
        .inOrder();
    assertEquals(map.headMap("three", true), map.descendingMap().tailMap("three", true));
    assertThat(map.tailMap("three", false).entrySet()).contains(mapEntry("two", 3));