* {@code combinations} does not retain the individual subsets.
   *
   * @param set the set of elements to take combinations of
   * @param size the number of elements per combination
   * @return the set of all combinations of {@code size} elements from {@code set}
   * @throws IllegalArgumentException if {@code size} is not between 0 and {@code set.size()}
   *     inclusive

     * expected</i>, but not absolutely required, to have the following properties:
     *
     * <ul>
     *   <li>Its execution does not cause any observable side effects.
     *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
     *       Objects.equal}{@code (k1, k2) &&} {@link Objects#equal}{@code (v1, v2)} implies that

   * expected</i>, but not absolutely required, to have the following properties:
   *
   * <ul>
   *   <li>Its execution does not cause any observable side effects.
   *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
   *       Objects.equal}{@code (a, b)} implies that {@code Objects.equal(function.apply(a),
   *       function.apply(b))}.
   * </ul>
   *