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(* GNU General Public License for more details.                       *)
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(* 02110-1301 USA                                                     *)
(* conservation de l'invariant de compatibilité par rapport à une signature pour l'union *)
(* conservation de l'invariant ref_ok pour l'union *)

Lemma union_mpl_correct_ref_ok_invar :
forall (s0 s1 : state) (d : preDTA),
state_ref_ok s0 d -> state_ref_ok s1 d -> state_ref_ok (union_mpl s0 s1) d.