src/HOL/Tools/BNF/bnf_lfp_compat.ML

             if member (op =) fpT_names T_name1 then
               nn_fp
             else
               (case Symtab.lookup all_infos T_name1 of
                 SOME {descr, ...} =>
-                length (filter_out (fn (_, (_, Us, _)) => exists Datatype_Aux.is_rec_type Us) descr)
+                length (filter_out (exists Datatype_Aux.is_rec_type o #2 o snd) descr)
               | NONE => raise Fail "unknown old-style datatype");
         in
           chop nn full_descr ||> cliquify_descr |> op ::
         end;