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diff --git a/matita/matita/contribs/lambdadelta/basic_2/dynamic/cnv_cpm_tdpos.ma b/matita/matita/contribs/lambdadelta/basic_2/dynamic/cnv_cpm_tdpos.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/tdpos.ma".
+include "basic_2/dynamic/cnv_cpm_tdeq.ma".
+
+(* CONTEXT-SENSITIVE NATIVE VALIDITY FOR TERMS ******************************)
+
+(* Forward lemmas with positive rt-transition for terms *********************)
+
+lemma cpm_tdeq_fwd_tdpos_sn (a) (h) (o) (n) (G):
+                            ∀L,T1. ⦃G,L⦄ ⊢ T1 ![a,h] →
+                            ∀T2. ⦃G,L⦄ ⊢ T1 ➡[n,h] T2 → T1 ≛[h,o] T2 → 𝐏[h,o]⦃T1⦄ →
+                            ∧∧ T1 = T2 & 0 = n.
+#a #h #o #n #G #L #T1 #H0 #T2 #H1 #H2
+@(cpm_tdeq_ind … H0 … H1 H2) -L -T1 -T2
+[ /2 width=1 by conj/
+| #L #s #_ #H1 #H
+  elim (tdpos_inv_sort … H) -H #d #H2
+  lapply (deg_mono … H2 H1) -H1 -H2 #H destruct
+| #p #I #L #V #T1 #_ #_ #T2 #_ #_ #IH #H
+  elim (tdpos_inv_pair … H) -H #_ #HT1
+  elim IH // -IH -HT1 #H1 #H2 destruct
+  /2 width=1 by conj/
+| #m #_ #L #V #_ #W #_ #q #T1 #U1 #_ #_ #T2 #_ #_ #IH #H -a -m -q -G -L -W -U1
+  elim (tdpos_inv_pair … H) -H #_ #HT1
+  elim IH // -IH -HT1 #H1 #H2 destruct
+  /2 width=1 by conj/
+| #L #U0 #U1 #T1 #_ #_ #U2 #_ #_ #_ #T2 #_ #_ #_ #IHU #IHT #H
+  elim (tdpos_inv_pair … H) -H #HU1 #HT1
+  elim IHU // -IHU -HU1 #H1 #H2 destruct
+  elim IHT // -IHT -HT1 #H1 #H2 destruct
+  /2 width=1 by conj/
+]
+qed-.
+
+lemma cpm_fwd_tdpos_sn (a) (h) (o) (n) (G) (L):
+                       ∀T1. ⦃G,L⦄ ⊢ T1 ![a,h] → 𝐏[h,o]⦃T1⦄ →
+                       ∀T2. ⦃G,L⦄ ⊢ T1 ➡[n,h] T2 →
+                       ∨∨ ∧∧ T1 = T2 & 0 = n | (T1 ≛[h,o] T2 → ⊥).
+#a #h #o #n #G #L #T1 #H1T1 #H2T1 #T2 #HT12
+elim (tdeq_dec h o T1 T2) #H
+/3 width=9 by cpm_tdeq_fwd_tdpos_sn, or_intror, or_introl/
+qed-.