let ap : all 'a 'b. ('a -> 'b) -> 'a -> 'b =
  fun 'a 'b ->
    fun f: ('a -> 'b) ->
      fun x: 'a ->
        f x

let inc : int -> int =
  fun y: int ->
    let g = (fun z:int  -> z + 1 : int -> int :> int -o int) in
      ap[int,int] g y    (* g: (int -o int) is used as an (int -> int) *)

in print[int] (inc 5)