private static final String LOWER = "abcdefghijklmnopqrstuvwxyz";
  private static final String UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  public void testToLowerCase() {
    assertEquals(LOWER, Ascii.toLowerCase(UPPER));
    assertSame(LOWER, Ascii.toLowerCase(LOWER));
    assertEquals(IGNORED, Ascii.toLowerCase(IGNORED));

   * can hold setSize elements with the desired load factor.
   */
  @VisibleForTesting
  static int chooseTableSize(int setSize) {
    if (setSize == 1) {
      return 2;
    }
    // Correct the size for open addressing to match desired load factor.
    // Round up to the next highest power of 2.
    int tableSize = Integer.highestOneBit(setSize - 1) << 1;

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

  @Override
  public E last() {
    return delegate.last();
  }

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

  @Override
  public @Nullable E pollFirst() {
    return delegate.pollFirst();
  }

  @Override
  public @Nullable E pollLast() {

  }

  @Override
  public E last() {
    if (isEmpty()) {
      throw new NoSuchElementException();
    }
    return elements.get(size() - 1);
  }

  @Override
  @CheckForNull
  public E lower(E element) {
    int index = headIndex(element, false) - 1;
    return (index == -1) ? null : elements.get(index);
  }

  @Override
  @CheckForNull
  public E floor(E element) {

        a full-time Guava team member. [Feedback](https://stackoverflow.com/a/4543114) from our
        users indicates that they really appreciate Guava's high power-to-weight ratio. It's
        important to us to keep Guava as easy to use and understand as we can. That means boiling
        features down to compact but powerful abstractions, and controlling feature bloat carefully.

  }

  @Override
  @GwtIncompatible("NavigableSet")
  ImmutableSortedSet<E> createDescendingSet() {
    throw new AssertionError("should never be called");
  }

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

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

  @Override
  @CheckForNull

    // key is not present
    int nextHigherIndex = list.size();
    for (int i = list.size() - 1; i >= 0 && list.get(i) > key; i--) {
      nextHigherIndex = i;
    }
    switch (absentBehavior) {
      case NEXT_LOWER:
        assertEquals(nextHigherIndex - 1, answer);
        return;
      case NEXT_HIGHER:
        assertEquals(nextHigherIndex, answer);
        return;
      case INVERTED_INSERTION_INDEX:

    // key is not present
    int nextHigherIndex = list.size();
    for (int i = list.size() - 1; i >= 0 && list.get(i) > key; i--) {
      nextHigherIndex = i;
    }
    switch (absentBehavior) {
      case NEXT_LOWER:
        assertEquals(nextHigherIndex - 1, answer);
        return;
      case NEXT_HIGHER:
        assertEquals(nextHigherIndex, answer);
        return;
      case INVERTED_INSERTION_INDEX:

        a full-time Guava team member. [Feedback](https://stackoverflow.com/a/4543114) from our
        users indicates that they really appreciate Guava's high power-to-weight ratio. It's
        important to us to keep Guava as easy to use and understand as we can. That means boiling
        features down to compact but powerful abstractions, and controlling feature bloat carefully.

  private static final String LOWER = "abcdefghijklmnopqrstuvwxyz";
  private static final String UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  public void testToLowerCase() {
    assertEquals(LOWER, Ascii.toLowerCase(UPPER));
    assertSame(LOWER, Ascii.toLowerCase(LOWER));
    assertEquals(IGNORED, Ascii.toLowerCase(IGNORED));