sicp exercise 1.9

;  Exercise 1.9.  Each of the following two procedures defines a method for adding two positive integers in
;  terms of the procedures inc, which increments its argument by 1, and dec, which decrements its argument
;  by 1.
;
;  (define (+ a b)
;    (if (= a 0)
;        b
;        (inc (+ (dec a) b))))
;
;  (define (+ a b)
;    (if (= a 0)
;        b
;        (+ (dec a) (inc b))))
;
;  Using the substitution model, illustrate the process generated by each procedure in evaluating (+ 4 5).
;  Are these processes iterative or recursive?


;  Answer:
;  The first procedure is recursive. The second one is iterative.