sicp exercise 1.20

;  Exercise 1.20.  The process that a procedure generates is of course dependent on the rules used by the
;  interpreter. As an example, consider the iterative gcd procedure given above. Suppose we were to interpret ;  this procedure using normal-order evaluation, as discussed in section 1.1.5. (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 remainder operations that are actually
;  performed. How many remainder operations are actually performed in the normal-order evaluation of
;  (gcd 206 40)? In the applicative-order evaluation?