@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) {

      return Maps.immutableEntry(entry.getKey(), unmodifiableCollectionSubclass(output));
    }

    @Override
    public NavigableMap<K, Collection<V>> descendingMap() {
      return new NavigableAsMap(sortedMap().descendingMap());
    }

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

    @Override

      super(delegate);
    }

    @Override
    public NavigableMap<K, V> create(Object... entries) {
      NavigableMap<K, V> map = (NavigableMap<K, V>) delegate.create(entries);
      return map.descendingMap();
    }

    @Override
    public Iterable<Entry<K, V>> order(List<Entry<K, V>> insertionOrder) {
      insertionOrder = castOrCopyToList(delegate.order(insertionOrder));
      reverse(insertionOrder);

      super(delegate);
    }

    @Override
    public NavigableMap<K, V> create(Object... entries) {
      NavigableMap<K, V> map = (NavigableMap<K, V>) delegate.create(entries);
      return map.descendingMap();
    }

    @Override
    public Iterable<Entry<K, V>> order(List<Entry<K, V>> insertionOrder) {
      insertionOrder = castOrCopyToList(delegate.order(insertionOrder));
      reverse(insertionOrder);

  }

  @CollectionSize.Require(SEVERAL)
  public void testDescendingNavigation() {
    List<Entry<K, V>> descending = new ArrayList<>(navigableMap.descendingMap().entrySet());
    Collections.reverse(descending);
    assertEquals(entries, descending);
  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapExclusive() {

    return new AsMapOfRanges(entriesByLowerBound.values());
  }

  @Override
  public Map<Range<K>, V> asDescendingMapOfRanges() {
    return new AsMapOfRanges(entriesByLowerBound.descendingMap().values());
  }

  private final class AsMapOfRanges extends IteratorBasedAbstractMap<Range<K>, V> {

    final Iterable<Entry<Range<K>, V>> entryIterable;

    assertEquals("one", map.floorKey("r"));
    assertEquals("three", map.floorKey("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));

    assertEquals("one", map.floorKey("r"));
    assertEquals("three", map.floorKey("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));