signature S =
sig
    type ar
    type elem
    val cons : int * elem -> ar
end

functor F(X : S) =
  struct 
  end

signature R = 
sig
    type 'a ar
    val cons : int * 'a -> 'a ar
end

structure N :> R =
struct
    type 'a ar = 'a Array.array
    val cons = Array.array
end

structure M = F(
	      struct open N
	      type elem = int
	      type ar = elem ar
	      end)