src/Pure/Isar/code_unit.ML

           |> Conjunction.intr_balanced
           |> f
           |> Conjunction.elim_balanced (length thms)
   in
     thms
-    |> burrow_thms (canonical_tvars thy purify_tvar)
     |> map (canonical_vars thy purify_var)
     |> map (canonical_absvars purify_var)
+    |> map Drule.zero_var_indexes
+    |> burrow_thms (canonical_tvars thy purify_tvar)
     |> Drule.zero_var_indexes_list
   end;
 
 
 (* const aliasses *)