}

  @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

  @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);
  }

  }

  @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

 * control. Under low update contention, the two classes have similar characteristics. But under
 * high contention, expected throughput of this class is significantly higher, at the expense of
 * higher space consumption.
 *
 * <p>This class extends {@link Number}, but does not define methods such as {@code

  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();

    /**
     * Gets the problems that were encountered during the settings building. Note that only problems of severity
     * {@link BuilderProblem.Severity#WARNING} and below are reported here. Problems with a higher severity level cause
     * the settings builder to fail with a {@link ToolchainsBuilderException}.
     *
     * @return the problems that were encountered during the settings building, can be empty but never {@code null}

      @Override
      int resultIndex(int higherIndex) {
        return higherIndex - 1;
      }
    },
    /**
     * Return the index of the next higher element in the list, or {@code list.size()} if there is
     * no such element.
     */
    NEXT_HIGHER {
      @Override
      public int resultIndex(int higherIndex) {
        return higherIndex;
      }
    },
    /**

      nextHigherIndex = i;
    }
    switch (absentBehavior) {
      case NEXT_LOWER:
        assertEquals(nextHigherIndex - 1, answer);
        return;
      case NEXT_HIGHER:
        assertEquals(nextHigherIndex, answer);
        return;
      case INVERTED_INSERTION_INDEX:
        assertEquals(-1 - nextHigherIndex, answer);
        return;
      default:

      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) {