62. Determine for each of the following classes of subsets of {I, ... , n} whether (together with the empty subset) it forms a group under the group operation of the preceding problem: All subsets {il , ... , if} with (i) r = 2; (ii) r = even; (iii) r divisible by 3. (iv) Give two other examples of subgroups Go of G. Note . A class of such subgroups is discussed by Forsythe and Hartigan (1970).