}

    @Override
    public @Nullable Entry<K, V> pollLastEntry() {
      return standardPollLastEntry();
    }

    @Override
    public NavigableMap<K, V> descendingMap() {
      return new StandardDescendingMap();
    }

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

    @Override

    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));