(def! abs (fn* [a]
    (if (> a 0)
        a
        (- 0 a))))

(def! mod (fn* [a b]
    (- a (* (/ a b) b))))

(def! max (fn* [a b]
    (if (> a b)
        a
        b)))

(def! min (fn* [a b]
    (if (< a b)
        a
        b)))

(def! fact (fn* [a]
    (def! fact-r (fn* [a b]
        (if (not (> a 1)) b
            (fact-r (- a 1) (* a b)))))
    (fact-r a 1)))