src/HOL/Tools/BNF/bnf_gfp_grec_sugar.ML

 
         val def_rhs = mk_corec_fun_def_rhs lthy7 arg_Ts corecUU0 corecUU_arg;
         val def = ((b, mx), ((Binding.concealed (Thm.def_binding b), []), def_rhs));
 
         val ((fun_lhs0, (_, fun_def0)), (lthy9, lthy8')) = lthy7
-          |> Local_Theory.open_target |> snd
+          |> Local_Theory.open_target
           |> Local_Theory.define def
           |> tap (fn (def, lthy') => print_def_consts int [def] lthy')
           ||> `Local_Theory.close_target;
 
         val parsed_eq = parse_corec_equation lthy9 [fun_free] eq;