@Override
  public abstract UnmodifiableIterator<E> descendingIterator();

  /** Returns the position of an element within the set, or -1 if not present. */
  abstract int indexOf(@CheckForNull Object target);

  /*
   * This class is used to serialize all ImmutableSortedSet instances,
   * regardless of implementation type. It captures their "logical contents"

  @Override
  public abstract UnmodifiableIterator<E> descendingIterator();

  /** Returns the position of an element within the set, or -1 if not present. */
  abstract int indexOf(@CheckForNull Object target);

  /*
   * This class is used to serialize all ImmutableSortedSet instances,
   * regardless of implementation type. It captures their "logical contents"

  @Override
  public boolean containsAll(Collection<?> targets) {
    for (Object target : targets) {
      if (target == null) {
        // This set never contains null.  We need to explicitly check here
        // because some comparator might throw NPE (e.g. the natural ordering).
        return false;
      }
    }
    try {
      return sortedDelegate.containsAll(targets);
    } catch (ClassCastException e) {