(func min (lst :{:int})
    (def val (first lst))
    (for-each (rest lst)
        (if (< _item_ val)
            (redef val _item_)))
    val)

(func lev (s t)
    (branch
        ((eq? 0 (length s)) (length t))
        ((eq? 0 (length t)) (length s))
        ((eq? (first s) (first t))
            (lev (rest s) (rest t)))
        (#true
            (+ 1
                (min
                    (list
                        (lev s (rest t))
                        (lev (rest s) t)
                        (lev (rest s) (rest t))))))))