(define $fib
  (lambda [$n]
    (match n Nat
      {[<o> 1]
       [<s <o>> 1]
       [<s <s $n1>> (+ (fib (+ n1 1)) (fib n1))]})))

(test (fib 10))

(define $fact
  (lambda [$n]
    (match n Nat
      {[<o> 1]
       [<s $n1> (* n (fact n1))]})))

(test (fact 10))

(define $min
  (lambda [$ns]
    (match ns (List Int)
      {[<cons $n <nil>> n]
       [<cons $n $rs>
        (let {[$r (min Rs)]}
          (match (compare-number n r) Order
            {[<less> n]
             [_ r]}))]})))

(define $gcd
  (lambda [$ns]
    (let {[$ns2 ((remove-all Int) ns 0)]}
      (match ns2 (Set Int)
        {[<cons $n <nil>> n]
         [<cons ,(min ns2)
                $rs>
          (gcd {n @(map (lambda [$r] (mod r n))
                        rs)})]}))))