[n] can thus be considered as a set of integers from 0 to n − 1.
one possible mapping is: π : {0, 1, 2, 3} → {3, 2, 1, 0} Here it means: π(0) = 3, π(1) = 2, π(2) = 1, π(3) = 0 Another possible mapping would be: π : {0, 1, 2, 3} → {3, 0, 1, 2} Here it means: π(0) = 3, π(1) = 0, π(2) = 1, π(3) = 2 for the set [4] there would be 4!