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sicp-all-tasks/sicp/1_002e9

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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?