5 Error message: This expression has type t <> 'a 'b, but is expected to have type t 'a1 'a2
7 Clone substitute every occurrence of the type by the logic version, while
8 we expect to use the program version in add.
22 type t = { ghost a : unit }
24 clone export A with type t = t
27 let sub (x:t) : unit = A.add x