; 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)
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