+let message3 m t1 t2 ?mu t3 =
+ let sm, st1, st2 = "In the context", "the term", "is of type" in
+ match mu with
+ | Some mu ->
+ let smu, st3 = "but in the context", "it must be of type" in
+ L.ct_items3 sm m st1 t1 st2 t2 ~sc3:smu ~c3:mu st3 t3
+ | None ->
+ let st3 = "but it must be of type" in
+ L.ct_items3 sm m st1 t1 st2 t2 st3 t3
+
+let error3 m t1 t2 ?mu t3 =
+ raise (TypeError (message3 m t1 t2 ?mu t3))
+
+let assert_convertibility f ~si m u w v =
+ let err _ = error3 m v w u in
+ R.are_convertible err f ~si m u m w
+
+let assert_applicability f ~si m u w v =
+ let f mu = function
+ | B.Bind (B.Abst (_, u), _) ->
+ let err _ = error3 m v w ~mu u in
+ R.are_convertible err f ~si mu u m w
+ | _ -> error1 "not a function type" m u
+ in
+ R.xwhd f m u