sicp exercise 3.9

; Exercise 3.9.  In section 1.2.1 we used the substitution model to analyze two procedures for computing factorials, a recursive version
;
; (define (factorial n)
;   (if (= n 1)
;       1
;       (* n (factorial (- n 1)))))
;
; and an iterative version
;
; (define (factorial n)
;   (fact-iter 1 1 n))
; (define (fact-iter product counter max-count)
;   (if (> counter max-count)
;       product
;       (fact-iter (* counter product)
;                  (+ counter 1)
;                  max-count)))
;
; Show the environment structures created by evaluating (factorial 6) using each version of the factorial procedure.