}

  @Override
  @CheckForNull
  public K floorKey(@ParametricNullness K key) {
    return Maps.keyOrNull(floorEntry(key));
  }

  @Override
  @CheckForNull
  public K ceilingKey(@ParametricNullness K key) {
    return Maps.keyOrNull(ceilingEntry(key));
  }

  @Override
  @CheckForNull
  public K higherKey(@ParametricNullness K key) {
    return Maps.keyOrNull(higherEntry(key));

    assertEquals(a, navigableMap.ceilingEntry(a.getKey()));
    assertEquals(a.getKey(), navigableMap.ceilingKey(a.getKey()));
    assertEquals(c, navigableMap.ceilingEntry(b.getKey()));
    assertEquals(c.getKey(), navigableMap.ceilingKey(b.getKey()));
    assertEquals(c, navigableMap.ceilingEntry(c.getKey()));
    assertEquals(c.getKey(), navigableMap.ceilingKey(c.getKey()));
  }

  @CollectionSize.Require(SEVERAL)
  public void testHigher() {

      return standardFloorKey(key);
    }

    @Override
    public @Nullable Entry<K, V> ceilingEntry(K key) {
      return standardCeilingEntry(key);
    }

    @Override
    public @Nullable K ceilingKey(K key) {
      return standardCeilingKey(key);
    }

    @Override
    public @Nullable Entry<K, V> higherEntry(K key) {
      return standardHigherEntry(key);
    }

    @Override

      return (entry == null) ? null : wrapEntry(entry);
    }

    @Override
    @CheckForNull
    public K ceilingKey(@ParametricNullness K key) {
      return sortedMap().ceilingKey(key);
    }

    @Override
    @CheckForNull
    public Entry<K, Collection<V>> higherEntry(@ParametricNullness K key) {

      @SuppressWarnings({"unchecked", "nullness"})
      SortedMap<@Nullable Object, V> self = (SortedMap<@Nullable Object, V>) this;
      Object ceilingKey = self.tailMap(key).firstKey();
      return unsafeCompare(comparator(), ceilingKey, key) == 0;
    } catch (ClassCastException | NoSuchElementException | NullPointerException e) {
      return false;
    }
  }

  /**

        return nullableSynchronizedEntry(delegate().ceilingEntry(key), mutex);
      }
    }

    @Override
    @CheckForNull
    public K ceilingKey(K key) {
      synchronized (mutex) {
        return delegate().ceilingKey(key);
      }
    }

    @CheckForNull transient NavigableSet<K> descendingKeySet;

    @Override
    public NavigableSet<K> descendingKeySet() {

      if (lowerEntry != null
          && lowerEntry.getValue().getUpperBound().compareTo(subRange.lowerBound) > 0) {
        lowerBound = subRange.lowerBound;
      } else {
        lowerBound = entriesByLowerBound.ceilingKey(subRange.lowerBound);
        if (lowerBound == null || lowerBound.compareTo(subRange.upperBound) >= 0) {
          throw new NoSuchElementException();
        }
      }

      Cut<K> upperBound;

    assertEquals("three", map.higherKey("one"));
    assertEquals("three", map.higherKey("r"));
    assertEquals("three", map.ceilingKey("r"));
    assertEquals("one", map.ceilingKey("one"));
    assertEquals(mapEntry("three", 5), map.higherEntry("one"));
    assertEquals(mapEntry("one", 3), map.ceilingEntry("one"));
    assertEquals("one", map.lowerKey("three"));

    assertEquals("three", map.higherKey("one"));
    assertEquals("three", map.higherKey("r"));
    assertEquals("three", map.ceilingKey("r"));
    assertEquals("one", map.ceilingKey("one"));
    assertEquals(mapEntry("three", 5), map.higherEntry("one"));
    assertEquals(mapEntry("one", 3), map.ceilingEntry("one"));
    assertEquals("one", map.lowerKey("three"));

      return transformEntry(fromMap().ceilingEntry(key));
    }

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

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

    @Override