Module Identifiable

module Identifiable: sig .. end

module type Thing = sig .. end

module Pair: 
functor (A : Thing) -> 
functor (B : Thing) -> Thing  with type t = A.t * B.t

module type Set = sig .. end

module type Map = sig .. end

module type Tbl = sig .. end

module type S = sig .. end

module Make: 
functor (T : Thing) -> S  with type t := T.t