### Exercises

#### Exercise 1.20.

The process that a function generates is of course dependent on the rules used by the interpreter. As an example, consider the iterative gcd/2 function given previously. Suppose we were to interpret this function using normal-order evaluation, as discussed in the section The Substitution Model for Function Application. (The normal-order-evaluation rule for if is described in exercise 1.5.) Using the substitution method (for normal order), illustrate the process generated in evaluating (gcd 206 40) and indicate the rem operations that are actually performed. How many rem operations are actually performed in the normal-order evaluation of (gcd 206 40)? In the applicative-order evaluation?