* @param self a collection which might contain all elements in {@code c}
   * @param c a collection whose elements might be contained by {@code self}
   */
  static boolean containsAllImpl(Collection<?> self, Collection<?> c) {
    for (Object o : c) {
      if (!self.contains(o)) {
        return false;
      }
    }
    return true;
  }

  /** An implementation of {@link Collection#toString()}. */

   * @param self a collection which might contain all elements in {@code c}
   * @param c a collection whose elements might be contained by {@code self}
   */
  static boolean containsAllImpl(Collection<?> self, Collection<?> c) {
    for (Object o : c) {
      if (!self.contains(o)) {
        return false;
      }
    }
    return true;
  }

  /** An implementation of {@link Collection#toString()}. */