(define (inc x)
  (+ x 1))

(define (dec x)
  (- x 1))

(define (+ a b)
  (display a)(newline)
  (if (= a 0)
      b
      (inc (+ (dec a) b))))

(+ 4 5)

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

(+ 4 5)