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diff --git a/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_drops.ma b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_drops.ma
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+++ b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cprs_drops.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 "basic_2/rt_computation/cpms_drops.ma".
+
+(* CONTEXT-SENSITIVE PARALLEL R-COMPUTATION FOR TERMS ***********************)
+
+(* Advanced inversion lemmas ************************************************)
+
+(* Basic_1: was: pr3_gen_lref *)
+(* Basic_2A1: was: cprs_inv_lref1 *)
+lemma cprs_inv_lref1_drops (h) (G): ∀L,T2,i. ⦃G, L⦄ ⊢ #i ➡*[h] T2 →
+                                    ∨∨ T2 = #i
+                                     | ∃∃K,V1,T1. ⬇*[i] L ≘ K.ⓓV1 & ⦃G, K⦄ ⊢ V1 ➡*[h] T1 &
+                                                  ⬆*[↑i] T1 ≘ T2.
+#h #G #L #T2 #i #H elim (cpms_inv_lref1_drops … H) -H *
+[ /2 width=1 by or_introl/
+| /3 width=6 by ex3_3_intro, or_intror/
+| #m #K #V #V2 #_ #_ #_ #H destruct
+]
+qed-.