(define (leap-year? y)
  (or (= (modulo y 400) 0)
      (and (= (modulo y 4) 0)
           (not (= (modulo y 100) 0)))))


(define (original-leap-year? y)
  (cond ((= (modulo y 400) 0) #t)
        ((= (modulo y 100) 0) #f)
        ((= (modulo y 4) 0) #t)
        (else #f)))