However, even if the method is clear, I run into problems trying to apply it on these 2 recursive modules :
map to sets and a set of map to sets.

module F ( X : Set.OrderedType ) = struct
  module rec Mod : sig 
    module XSet :
      sig
        type elt = X.t
        type t = Set.Make( X ).t
      end
    module XMap :
      sig
        type key = X.t
        type 'a t = 'a Map.Make( X ).t
      end
    type elt = X.t
    type t = XSet.t XMap.t
  end
     =
  struct
    module XSet = Set.Make( X )
    module XMap = Map.Make( X )

    type elt = X.t
    type t = XSet.t XMap.t
  end
  and ModSet : Set.S with type elt = Mod.t = Set.Make( Mod )
end

Got this internal message from ocaml 3.10.1 :
"Fatal error: exception Assert_failure("typing/path.ml", 48, 22)"

Maybe should the a' type be declared (as XSet.t) ?

Any light ?

Fabrice