+(**************************************************************************)
+(* ___ *)
+(* ||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/fpbg.ma".
+include "basic_2/rt_computation/cpms_fpbs.ma".
+include "basic_2/dynamic/cnv.ma".
+
+(* CONTEXT-SENSITIVE NATIVE VALIDITY FOR TERMS ******************************)
+
+(* Inductive premises for the preservation results **************************)
+
+definition IH_cnv_cpm_trans_lpr (a) (h): relation3 genv lenv term ≝
+ λG,L1,T1. ⦃G, L1⦄ ⊢ T1 ![a,h] →
+ ∀n,T2. ⦃G, L1⦄ ⊢ T1 ➡[n,h] T2 →
+ ∀L2. ⦃G, L1⦄ ⊢ ➡[h] L2 → ⦃G, L2⦄ ⊢ T2 ![a,h].
+
+definition IH_cnv_cpms_trans_lpr (a) (h): relation3 genv lenv term ≝
+ λG,L1,T1. ⦃G, L1⦄ ⊢ T1 ![a,h] →
+ ∀n,T2. ⦃G, L1⦄ ⊢ T1 ➡*[n,h] T2 →
+ ∀L2. ⦃G, L1⦄ ⊢ ➡[h] L2 → ⦃G, L2⦄ ⊢ T2 ![a,h].
+
+definition IH_cnv_cpm_conf_lpr (a) (h): relation3 genv lenv term ≝
+ λG,L0,T0. ⦃G, L0⦄ ⊢ T0 ![a,h] →
+ ∀n1,T1. ⦃G, L0⦄ ⊢ T0 ➡[n1,h] T1 → ∀n2,T2. ⦃G, L0⦄ ⊢ T0 ➡[n2,h] T2 →
+ ∀L1. ⦃G, L0⦄ ⊢ ➡[h] L1 → ∀L2. ⦃G, L0⦄ ⊢ ➡[h] L2 →
+ ∃∃T. ⦃G, L1⦄ ⊢ T1 ➡*[n2-n1,h] T & ⦃G, L2⦄ ⊢ T2 ➡*[n1-n2,h] T.
+
+definition IH_cnv_cpms_strip_lpr (a) (h): relation3 genv lenv term ≝
+ λG,L0,T0. ⦃G, L0⦄ ⊢ T0 ![a,h] →
+ ∀n1,T1. ⦃G, L0⦄ ⊢ T0 ➡*[n1,h] T1 → ∀n2,T2. ⦃G, L0⦄ ⊢ T0 ➡[n2,h] T2 →
+ ∀L1. ⦃G, L0⦄ ⊢ ➡[h] L1 → ∀L2. ⦃G, L0⦄ ⊢ ➡[h] L2 →
+ ∃∃T. ⦃G, L1⦄ ⊢ T1 ➡*[n2-n1,h] T & ⦃G, L2⦄ ⊢ T2 ➡*[n1-n2,h] T.
+
+definition IH_cnv_cpms_conf_lpr (a) (h): relation3 genv lenv term ≝
+ λG,L0,T0. ⦃G, L0⦄ ⊢ T0 ![a,h] →
+ ∀n1,T1. ⦃G, L0⦄ ⊢ T0 ➡*[n1,h] T1 → ∀n2,T2. ⦃G, L0⦄ ⊢ T0 ➡*[n2,h] T2 →
+ ∀L1. ⦃G, L0⦄ ⊢ ➡[h] L1 → ∀L2. ⦃G, L0⦄ ⊢ ➡[h] L2 →
+ ∃∃T. ⦃G, L1⦄ ⊢ T1 ➡*[n2-n1,h] T & ⦃G, L2⦄ ⊢ T2 ➡*[n1-n2,h] T.
+
+(* Auxiliary properties for preservation ************************************)
+
+fact cnv_cpms_trans_lpr_sub (a) (h) (o):
+ ∀G0,L0,T0.
+ (∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpm_trans_lpr a h G1 L1 T1) →
+ ∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpms_trans_lpr a h G1 L1 T1.
+#a #h #o #G0 #L0 #T0 #IH #G1 #L1 #T1 #H01 #HT1 #n #T2 #H
+@(cpms_ind_dx … H) -n -T2
+/4 width=7 by cpms_fwd_fpbs, fpbg_fpbs_trans/
+qed-.
+
+fact cnv_cpm_conf_lpr_sub (a) (h) (o):
+ ∀G0,L0,T0.
+ (∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpms_conf_lpr a h G1 L1 T1) →
+ ∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpm_conf_lpr a h G1 L1 T1.
+/3 width=8 by cpm_cpms/ qed-.
+
+fact cnv_cpms_strip_lpr_sub (a) (h) (o):
+ ∀G0,L0,T0.
+ (∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpms_conf_lpr a h G1 L1 T1) →
+ ∀G1,L1,T1. ⦃G0, L0, T0⦄ >[h, o] ⦃G1, L1, T1⦄ → IH_cnv_cpms_strip_lpr a h G1 L1 T1.
+/3 width=8 by cpm_cpms/ qed-.