*
   * <p>An empty iterable has only one permutation, which is an empty list.
   *
   * <p>This method is equivalent to {@code Collections2.orderedPermutations(list,
   * Ordering.natural())}.
   *
   * @param elements the original iterable whose elements have to be permuted.
   * @return an immutable {@link Collection} containing all the different permutations of the
   *     original iterable.

   *
   * <p>An empty iterable has only one permutation, which is an empty list.
   *
   * <p>This method is equivalent to {@code Collections2.orderedPermutations(list,
   * Ordering.natural())}.
   *
   * @param elements the original iterable whose elements have to be permuted.
   * @return an immutable {@link Collection} containing all the different permutations of the
   *     original iterable.