Recommended exercises from Section 7.5

I recommend  exercise 3, 4 and 5 (pp. 234-235).  These  are good (and quite hard) exercises that do not relate to the technical stuff in Section 7.5 (exercise 1 and 2 at page 234 are easy, but they require that you know the  know the technical stuff).

Exercise 6 (p. 235) is a hard exercise on the Ackermann function. It is an exercise for those who need an extra challenge.