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(* as published by the Free Software Foundation; either version 2.1   *)
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(*                                                                    *)
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(* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the      *)
(* 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 MapMerge_ref_ok_invar :
forall d0 d1 : preDTA,
preDTA_ref_ok d0 -> preDTA_ref_ok d1 -> preDTA_ref_ok (MapMerge state d0 d1).