pr9.spl

let postfix (post:set word:string):set = 
    (if (seteq post {})
    then {}
    else (cons (strapp word (head post)) (postfix (tail post) word)))
;;

let union (first:set second:set):set = 
    (if (seteq first {}) 
    then (if (seteq second {}) then {} else (union second {}))
    else (cons (head first) (union (tail first) second)))
;;

let concatenate(lang:set post:set):set = 
    (if (seteq lang {}) then {} else
    (union (postfix post (head lang))
           (concatenate (tail lang) post)))
;;

let restrict (ins:set num:int):set = 
    (if (== num 0) then {}
    else (if (seteq ins {}) then {}
          else (cons (head ins) (restrict (tail ins) (- num 1)))))
;;

let abset:set = {"a", "b"};;

(restrict (sort (concatenate (union arg0 arg1) abset)) maxoutput);;