(let a 4)
(let b 5)

(assert (= (+ a b) 9) "sum")
(assert (= (- a b) -1) "difference")
(assert (= (- b a) 1) "difference")
(assert (= (* a b) 20) "product")
(assert (= (/ a b) 0.8) "quotient")
(assert (= (mod a b) 4) "remainder(a, b)")
(assert (= (mod b a) 1) "remainder(b, a)")