; leap year

(define (leap? n)
  (if (positive? (modulo n 4)) #f
    (if (positive? (modulo n 100)) #t
      (if (positive? (modulo n 400)) #f
        #t))))

(display (leap? 2018)) (newline)
(display (leap? 2016)) (newline)
(display (leap? 2000)) (newline)
(display (leap? 2100)) (newline)