src/HOL/Tools/TFL/usyntax.ML

  *
  *                            Types
  *
  *---------------------------------------------------------------------------*)
 val mk_prim_vartype = TVar;
-fun mk_vartype s = mk_prim_vartype ((s, 0), HOLogic.typeS);
+fun mk_vartype s = mk_prim_vartype ((s, 0), @{sort type});
 
 (* But internally, it's useful *)
 fun dest_vtype (TVar x) = x
   | dest_vtype _ = raise USYN_ERR "dest_vtype" "not a flexible type variable";