Each of the following two procedures defines a method for adding two positive integers in terms of the procedures
, which increments its argument by 1, and
, 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?
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