src/HOL/Tools/inductive_set.ML

     val thm' = Thm.instantiate ([], insts) thm;
     val thm'' = (case optfs' of
         NONE => thm' RS sym
       | SOME fs' =>
           let
-            val U = List.last (binder_types T);
+            val U = HOLogic.dest_setT (body_type T);
             val Ts = HOLogic.strip_ptupleT fs' U;
             (* FIXME: should cterm_instantiate increment indexes? *)
             val arg_cong' = Thm.incr_indexes (Thm.maxidx_of thm + 1) arg_cong;
             val (arg_cong_f, _) = arg_cong' |> cprop_of |> Drule.strip_imp_concl |>
               Thm.dest_comb |> snd |> Drule.strip_comb |> snd |> hd |> Thm.dest_comb

     eta_contract_thm (is_pred pred_arities) |>
     Rule_Cases.save thm
   end;
 
 val to_pred_att = Thm.rule_attribute o to_pred;
-    
+
 
 (**** convert theorem in predicate notation to set notation ****)
 
 fun to_set thms ctxt thm =
   let

       | infer (Const (@{const_name Set.member}, _) $ t $ u) =
           infer_arities thy set_arities (SOME (HOLogic.flat_tuple_paths t), u)
       | infer (t $ u) = infer t #> infer u
       | infer _ = I;
     val new_arities = filter_out
-      (fn (x as Free (_, T), _) => member (op =) params x andalso length (binder_types T) > 1
+      (fn (x as Free (_, T), _) => member (op =) params x andalso length (binder_types T) > 0
         | _ => false) (fold (snd #> infer) intros []);
     val params' = map (fn x =>
       (case AList.lookup op = new_arities x of
         SOME fs =>
           let

 
     (* equations for converting sets to predicates *)
     val ((cs', cs_info), eqns) = cs |> map (fn c as Free (s, T) =>
       let
         val fs = the_default [] (AList.lookup op = new_arities c);
-        val (Us, U) = split_last (binder_types T);
+        val (Us, U) = strip_type T |> apsnd HOLogic.dest_setT;
         val _ = Us = paramTs orelse error (Pretty.string_of (Pretty.chunks
           [Pretty.str "Argument types",
            Pretty.block (Pretty.commas (map (Syntax.pretty_typ lthy) Us)),
            Pretty.str ("of " ^ s ^ " do not agree with types"),
            Pretty.block (Pretty.commas (map (Syntax.pretty_typ lthy) paramTs)),