; (define (product term a next b)
;   (if (> a b)
;       1
;       (* (term a)
;          (product term (next a) next b))))

(define (product term a next b)
  (define (iter a result)
    (if (= a b)
      (* (term a) result)
      (iter (next a) (* (term a) result))
     )
    )
  (iter a 1)
  )

(define (factorial n)
  (product * 1 inc n)
  )