}

  @Override
  public @Nullable E ceiling(E element) {
    int index = tailIndex(element, true);
    return (index == size()) ? null : elements.get(index);
  }

  @Override
  public @Nullable E higher(E element) {
    int index = tailIndex(element, false);
    return (index == size()) ? null : elements.get(index);
  }

  @Override

  }

  @Override
  public @Nullable E ceiling(E element) {
    int index = tailIndex(element, true);
    return (index == size()) ? null : elements.get(index);
  }

  @Override
  public @Nullable E higher(E element) {
    int index = tailIndex(element, false);
    return (index == size()) ? null : elements.get(index);
  }

  @Override

            E tail = head;
            int tailIndex = headIndex;
            for (E e = next; e != null; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              if (newIndex != tailIndex) {
                // The index changed. We'll need to copy the previous entry.
                tailIndex = newIndex;
                tail = e;
              }
            }

            E tail = head;
            int tailIndex = headIndex;
            for (E e = next; e != null; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              if (newIndex != tailIndex) {
                // The index changed. We'll need to copy the previous entry.
                tailIndex = newIndex;
                tail = e;
              }
            }

            ReferenceEntry<K, V> tail = head;
            int tailIndex = headIndex;
            for (ReferenceEntry<K, V> e = next; e != null; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              if (newIndex != tailIndex) {
                // The index changed. We'll need to copy the previous entry.
                tailIndex = newIndex;
                tail = e;
              }

            ReferenceEntry<K, V> tail = head;
            int tailIndex = headIndex;
            for (ReferenceEntry<K, V> e = next; e != null; e = e.getNext()) {
              int newIndex = e.getHash() & newMask;
              if (newIndex != tailIndex) {
                // The index changed. We'll need to copy the previous entry.
                tailIndex = newIndex;
                tail = e;
              }

   * the original {@code fromKey}.
   *
   * @since 12.0
   */
  @Override
  public ImmutableSortedMap<K, V> tailMap(K fromKey, boolean inclusive) {
    return getSubMap(keySet.tailIndex(checkNotNull(fromKey), inclusive), size());
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(K key) {
    return headMap(key, false).lastEntry();
  }

  @Override

   * the original {@code fromKey}.
   *
   * @since 12.0
   */
  @Override
  public ImmutableSortedMap<K, V> tailMap(K fromKey, boolean inclusive) {
    return getSubMap(keySet.tailIndex(checkNotNull(fromKey), inclusive), size());
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(K key) {
    return headMap(key, false).lastEntry();
  }

  @Override