; (define (+ a b)
;   (if (= a 0)
;       b
;       (inc (+ (dec a) b))))

; (+ 4 5)
; (inc (+ (dec 4) 5))
; (inc (+ 3 5))
; (inc (inc (+ 2 5)))
; (inc (inc (inc (+ 1 5))))
; (inc (inc (inc (inc (+ 0 5)))))
; (inc (inc (inc (inc 5))))
; (inc (inc (inc 6)))
; (inc (inc 7))
; (inc 8)
; > 9
; Recursive process

; (define (+ a b)
;   (if (= a 0)
;       b
;       (+ (dec a) (inc b))))

; (+ 4 5)
; (+ (dec 4) (inc 5))
; (+ 3 6)
; (+ 2 7)
; (+ 1 8)
; (+ 0 9)
; > 9
; Iterative process