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() {

    }
  }

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

  @Override
  public @Nullable K ceilingKey(K key) {
    return delegate.ceilingKey(checkValid(key));
  }

  @Override
  public void clear() {
    delegate.clear();
  }

  @Override
  public Comparator<? super K> comparator() {

    }
  }

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

  @Override
  public @Nullable K ceilingKey(K key) {
    return delegate.ceilingKey(checkValid(key));
  }

  @Override
  public void clear() {
    delegate.clear();
  }

  @Override
  public Comparator<? super K> comparator() {

  }

  @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));

  }

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

  /**
   * A sensible definition of {@link #ceilingKey} in terms of {@code ceilingEntry}. If you override
   * {@code ceilingEntry}, you may wish to override {@code ceilingKey} to forward to this
   * implementation.
   */
  @CheckForNull

  }

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

  /**
   * A sensible definition of {@link #ceilingKey} in terms of {@code ceilingEntry}. If you override
   * {@code ceilingEntry}, you may wish to override {@code ceilingKey} to forward to this
   * implementation.
   */
  @CheckForNull

  }

  @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 (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) {

        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() {