+(**************************************************************************)
+(* ___ *)
+(* ||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/equivalence/cpcs_cpcs.ma".
+include "basic_2/dynamic/lsubsv_ldrop.ma".
+
+(* LOCAL ENVIRONMENT REFINEMENT FOR STRATIFIED NATIVE VALIDITY **************)
+
+(* Properties on stratified native type assignment **************************)
+
+lemma lsubsv_ssta_trans: ∀h,g,L2,T,U2,l. ⦃h, L2⦄ ⊢ T •[g,l] U2 →
+ ∀L1. h ⊢ L1 ⊩:⊑[g] L2 →
+ ∃∃U1. L1 ⊢ U2 ⬌* U1 & ⦃h, L1⦄ ⊢ T •[g,l] U1.
+#h #g #L2 #T #U2 #l #H elim H -L2 -T -U2 -l
+[ #L2 #k #l #Hkl #L1 #_ /3 width=3/
+| #L2 #K2 #V2 #W2 #U2 #i #l #HLK2 #_ #HWU2 #IHVW2 #L1 #HL12
+ elim (lsubsv_ldrop_O1_trans … HL12 … HLK2) -L2 #X #H #HLK1
+ elim (lsubsv_inv_pair2 … H) -H *
+ [ #K1 #HK12 #H destruct
+ elim (IHVW2 … HK12) -K2 #W1 #HW21 #H
+ elim (lift_total W1 0 (i+1)) #U1 #HWU1
+ lapply (ldrop_fwd_ldrop2 … HLK1) /3 width=9/
+ | #K1 #V1 #W1 #l0 #_ #_ #_ #_ #_ #_ #H destruct
+ ]
+| #L2 #K2 #W2 #V2 #U2 #i #l #HLK2 #_ #HWU2 #IHWV2 #L1 #HL12
+ elim (lsubsv_ldrop_O1_trans … HL12 … HLK2) -L2 #X #H #HLK1
+ elim (lsubsv_inv_pair2 … H) -H *
+ [ #K1 #HK12 #H destruct
+ elim (IHWV2 … HK12) -K2 #V1 #_ #H -V2 /3 width=6/
+ | #K1 #W1 #V1 #l0 #HV1 #HVW1 #HW21 #HW2 #HK12 #H #_ destruct
+ elim (IHWV2 … HK12) -K2 #V #_ #H
+ elim (lift_total W1 0 (i+1)) #U1 #HWU1
+ lapply (ldrop_fwd_ldrop2 … HLK1) #HLK
+ @(ex2_intro … U1)
+ [ @(cpcs_lift … HLK … HWU2 … HWU1 HW21)
+ | @(ssta_ldef … HLK1 … HWU1)
+ (*
+ /3 width=9/
+ *)
\ No newline at end of file