src/HOL/Codatatype/Tools/bnf_lfp.ML

     val timer = time (Timer.startRealTimer ());
     val live = live_of_bnf (hd bnfs);
     val n = length bnfs; (*active*)
     val ks = 1 upto n;
     val m = live - n; (*passive, if 0 don't generate a new bnf*)
-    val b = Binding.name (fold_rev (fn b => fn s => Binding.name_of b ^ s) bs "");
+    val b = Binding.name (mk_bundle_name bs);
 
     (* TODO: check if m, n etc are sane *)
 
     val deads = fold (union (op =)) Dss resDs;
     val names_lthy = fold Variable.declare_typ deads lthy;