(* This program is free software; you can redistribute it and/or      *)
(* modify it under the terms of the GNU Lesser General Public License *)
(* as published by the Free Software Foundation; either version 2.1   *)
(* of the License, or (at your option) any later version.             *)
(*                                                                    *)
(* This program is distributed in the hope that it will be useful,    *)
(* but WITHOUT ANY WARRANTY; without even the implied warranty of     *)
(* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the      *)
(* GNU General Public License for more details.                       *)
(*                                                                    *)
(* You should have received a copy of the GNU Lesser General Public   *)
(* License along with this program; if not, write to the Free         *)
(* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA *)
(* 02110-1301 USA                                                     *)
(* invariant pour le kill_empty states de correction par rapport a une signature *)
(* invariant sur ref_ok pour le kill_empty *)

Lemma preDTA_kill_ref_ok_invar :
forall (d : preDTA) (sigma : signature),
preDTA_ref_ok d ->
predta_correct_wrt_sign d sigma ->
preDTA_ref_ok (preDTA_kill (dta_non_empty_states d) d).