# module type S = sig type u type t end
# module type S' = sig type t = int type u = bool end
#   *   val f : (module S with type t = int and type u = bool) -> (module S') = <fun>
# val g : (module S with type t = int and type u = bool) -> (module S') = <fun>
#     module type S2 = sig type u type t type w end
# val g2 : (module S2 with type t = int and type u = bool) -> (module S') =
  <fun>
# val h : (module S2 with type t = 'a) -> (module S with type t = 'a) = <fun>
#   Characters 63-64:
    (x : (module S'));; (* fail *)
     ^
Error: This expression has type
         (module S2 with type t = int and type u = bool)
       but an expression was expected of type (module S')
#   Characters 46-47:
    (x : (module S with type t = 'a));; (* fail *)
     ^
Error: This expression has type (module S2 with type t = 'a)
       but an expression was expected of type (module S with type t = 'a)
#     module type S3 = sig type u type t val x : int end
#   Characters 13-78:
    (x : (module S3 with type t = 'a and type u = 'b) :> (module S'));; (* fail *)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: Type (module S3 with type t = int and type u = bool)
       is not a subtype of (module S') 
#