type ('a, 'b) prod = 
    Pair of 'a * 'b ;;

type ('a) list = 
    Cons of 'a * ('a) list 
  | Nil ;;

let HD = 
  (fun x1 -> 
    (match x1 with 
        Nil -> (raise (Match_failure (string_of_bool true, 0, 0))) 
      | (Cons (v2, v1)) -> v2)) ;;

let TL = 
  (fun x1 -> 
    (match x1 with 
        Nil -> (raise (Match_failure (string_of_bool true, 0, 0))) 
      | (Cons (v2, v1)) -> v1)) ;;

let rec APPEND v3 = 
  (fun v4 -> 
    (match v3 with 
        Nil -> v4 
      | (Cons (v2, v1)) -> (Cons (v2, ((APPEND v1) v4))))) ;;

let rec REV v3 = 
  (fun v4 -> 
    (match v3 with 
        Nil -> v4 
      | (Cons (v2, v1)) -> ((REV v1) (Cons (v2, v4))))) ;;

let REVERSE = 
  (fun v1 -> ((REV v1) Nil)) ;;