File "pr4791.ml", line 1:
Warning 63 [erroneous-printed-signature]: The printed interface differs from
  the inferred interface. The inferred interface contained items which could
  not be printed properly due to name collisions between identifiers.
  File "pr4791.ml", line 11, characters 2-12:
  Definition of type t
File "pr4791.ml", line 8, characters 0-10:
  Definition of type t/2
  Beware that this warning is purely informational and will not catch all
  instances of erroneous printed interface.
type t = A
module B : sig type t = B val f : t/2 -> t end