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diff --git a/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_tweq.ma b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_tweq.ma
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+++ b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_tweq.ma
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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||         The HELM team.                                      *)
+(*      ||A||         http://helm.cs.unibo.it                             *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU General Public License Version 2                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "static_2/syntax/tweq_tweq.ma".
+include "static_2/relocation/lifts_tweq.ma".
+include "basic_2/rt_transition/cpr_drops_basic.ma".
+include "basic_2/rt_computation/cpms.ma".
+
+(* CONTEXT-SENSITIVE PARALLEL R-COMPUTATION FOR TERMS ***********************)
+
+(* Properties with sort-irrelevant whd equivalence on terms *****************)
+
+lemma cprs_abbr_pos_twneq (h) (G) (L) (V) (T1):
+      ∃∃T2. ⦃G,L⦄ ⊢ +ⓓV.T1 ➡*[h] T2 & (+ⓓV.T1 ≅ T2 → ⊥).
+#h #G #L #V #U1
+elim (cpr_subst h G (L.ⓓV) U1 … 0) [|*: /2 width=4 by drops_refl/ ] #U2 #T2 #HU12 #HTU2
+elim (tweq_dec U1 U2) [ #HpU12 | -HTU2 #HnU12 ]
+[ @(ex2_intro … T2) (**) (* full auto not tried *)
+  [ /3 width=6 by cpms_zeta, cpms_step_sn, cpm_bind/
+  | /4 width=6 by tweq_inv_abbr_pos_x_lifts_y_y, tweq_canc_sn, tweq_abbr_pos/
+  ]
+| /4 width=3 by cpm_cpms, cpm_bind, tweq_inv_abbr_pos_bi, ex2_intro/
+]
+qed-.