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(* as published by the Free Software Foundation; either version 2.1   *)
(* of the License, or (at your option) any later version.             *)
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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                                                     *)
Require Export DistributedReferenceCounting.machine4.invariant6.
Unset Standard Proposition Elimination Names.
(* Minute changes - in 1, deleted n0 - in 6, added n0 in initial Intros n0->n1, n1->2 - optim1 and optim2  *)

Lemma parent_invariant :
forall c : Config,
legal c ->
forall s : Site,
indirect_son1 c s -> exists s1 : Site, direct_son c s1 /\ ancestor c s1 s.