}

  @CollectionSize.Require(SEVERAL)
  public void testHigherHole() {
    resetWithHole();
    assertEquals(c, navigableSet.higher(a));
    assertEquals(c, navigableSet.higher(b));
    assertEquals(null, navigableSet.higher(c));
  }

  /*
   * TODO(cpovirk): make "too small" and "too large" elements available for better navigation

  }

  @CollectionSize.Require(SEVERAL)
  public void testHigherHole() {
    resetWithHole();
    assertEquals(c, navigableSet.higher(a));
    assertEquals(c, navigableSet.higher(b));
    assertEquals(null, navigableSet.higher(c));
  }

  /*
   * TODO(cpovirk): make "too small" and "too large" elements available for better navigation

  }

  @Override
  @CheckForNull
  public E higher(@ParametricNullness E e) {
    return delegate().higher(e);
  }

  /**
   * A sensible definition of {@link #higher} in terms of the {@code iterator} method of {@link
   * #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may wish to
   * override {@link #higher} to forward to this implementation.
   */
  @CheckForNull

  }

  @Override
  @CheckForNull
  public E higher(@ParametricNullness E e) {
    return delegate().higher(e);
  }

  /**
   * A sensible definition of {@link #higher} in terms of the {@code iterator} method of {@link
   * #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may wish to
   * override {@link #higher} to forward to this implementation.
   */
  @CheckForNull

      return emptySet(comparator());
    }
  }

  @CheckForNull
  E higher(E e) {
    checkNotNull(e);
    Iterator<E> iterator = tailSet(e).iterator();
    while (iterator.hasNext()) {
      E higher = iterator.next();
      if (comparator().compare(e, higher) < 0) {
        return higher;
      }
    }
    return null;
  }

  @CheckForNull
  public E ceiling(E e) {

  @CheckForNull
  public E lower(E element) {
    return forward.higher(element);
  }

  @Override
  @CheckForNull
  public E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  @CheckForNull
  public E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  @CheckForNull
  public E higher(E element) {
    return forward.lower(element);
  }

//     Vendors might change the settings based on the configuration and scale out of the solution (more storage nodes =>
//     higher task limit).
//
//     <S3ConcurrentTaskLimit>
//
//   - Defines how many S3 operations are executed parallel within one Repository Task Slot (and within one backup object

  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
    return new SafeTreeSet<>(delegate.headSet(checkValid(toElement), inclusive));
  }

  @Override
  public @Nullable E higher(E e) {
    return delegate.higher(checkValid(e));
  }

  @Override
  public boolean isEmpty() {
    return delegate.isEmpty();
  }

  @Override
  public Iterator<E> iterator() {
    return delegate.iterator();

  @CheckForNull
  public E lower(E element) {
    return forward.higher(element);
  }

  @Override
  @CheckForNull
  public E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  @CheckForNull
  public E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  @CheckForNull
  public E higher(E element) {
    return forward.lower(element);
  }

  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
    return new SafeTreeSet<>(delegate.headSet(checkValid(toElement), inclusive));
  }

  @Override
  public @Nullable E higher(E e) {
    return delegate.higher(checkValid(e));
  }

  @Override
  public boolean isEmpty() {
    return delegate.isEmpty();
  }

  @Override
  public Iterator<E> iterator() {
    return delegate.iterator();