; a twisted version of the code from p.91 at bottom

(define numr
  (lambda (rtl)
    (cdr rtl)))

(define denr
  (lambda (rtl)
    (car rtl)))

(define make-ratl
  (lambda (int1 int2)
    (if (zero? int2)
        (error "make-ratl: The denominator cannot be zero.")
        (cons int2 int1))))