he genre-counting problem (Example 9.24) considered a function f : {1, 2, . . . , n} → {1, 2, 3, 4, 5}. When n = 5 . . .
1 How many different functions f : {1, 2, . . . , 5} → {1, 2, . . . , 5} are there?
2 How many one-to-one functions f : {1, 2, . . . , 5} → {1, 2, . . . , 5} are there?
3 How many bijections f : {1, 2, . . . , 5} → {1, 2, . . . , 5} are there?
