--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||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/relocation/drops.ma".
+include "static_2/static/lsuba.ma".
+
+(* RESTRICTED REFINEMENT FOR ATOMIC ARITY ASSIGNMENT ************************)
+
+(* Properties with generic slicing for local environments *******************)
+
+(* Note: the premise 𝐔⦃f⦄ cannot be removed *)
+(* Basic_2A1: includes: lsuba_drop_O1_conf *)
+lemma lsuba_drops_conf_isuni: ∀G,L1,L2. G ⊢ L1 ⫃⁝ L2 →
+ ∀b,f,K1. 𝐔⦃f⦄ → ⬇*[b, f] L1 ≘ K1 →
+ ∃∃K2. G ⊢ K1 ⫃⁝ K2 & ⬇*[b, f] L2 ≘ K2.
+#G #L1 #L2 #H elim H -L1 -L2
+[ /2 width=3 by ex2_intro/
+| #I #L1 #L2 #HL12 #IH #b #f #K1 #Hf #H
+ elim (drops_inv_bind1_isuni … Hf H) -Hf -H *
+ [ #Hf #H destruct -IH
+ /3 width=3 by lsuba_bind, drops_refl, ex2_intro/
+ | #g #Hg #HLK1 #H destruct -HL12
+ elim (IH … Hg HLK1) -L1 -Hg /3 width=3 by drops_drop, ex2_intro/
+ ]
+| #L1 #L2 #W #V #A #HV #HW #HL12 #IH #b #f #K1 #Hf #H
+ elim (drops_inv_bind1_isuni … Hf H) -Hf -H *
+ [ #Hf #H destruct -IH
+ /3 width=3 by drops_refl, lsuba_beta, ex2_intro/
+ | #g #Hg #HLK1 #H destruct -HL12
+ elim (IH … Hg HLK1) -L1 -Hg /3 width=3 by drops_drop, ex2_intro/
+ ]
+]
+qed-.
+
+(* Note: the premise 𝐔⦃f⦄ cannot be removed *)
+(* Basic_2A1: includes: lsuba_drop_O1_trans *)
+lemma lsuba_drops_trans_isuni: ∀G,L1,L2. G ⊢ L1 ⫃⁝ L2 →
+ ∀b,f,K2. 𝐔⦃f⦄ → ⬇*[b, f] L2 ≘ K2 →
+ ∃∃K1. G ⊢ K1 ⫃⁝ K2 & ⬇*[b, f] L1 ≘ K1.
+#G #L1 #L2 #H elim H -L1 -L2
+[ /2 width=3 by ex2_intro/
+| #I #L1 #L2 #HL12 #IH #b #f #K2 #Hf #H
+ elim (drops_inv_bind1_isuni … Hf H) -Hf -H *
+ [ #Hf #H destruct -IH
+ /3 width=3 by lsuba_bind, drops_refl, ex2_intro/
+ | #g #Hg #HLK2 #H destruct -HL12
+ elim (IH … Hg HLK2) -L2 -Hg /3 width=3 by drops_drop, ex2_intro/
+ ]
+| #L1 #L2 #W #V #A #HV #HW #HL12 #IH #b #f #K2 #Hf #H
+ elim (drops_inv_bind1_isuni … Hf H) -Hf -H *
+ [ #Hf #H destruct -IH
+ /3 width=3 by drops_refl, lsuba_beta, ex2_intro/
+ | #g #Hg #HLK2 #H destruct -HL12
+ elim (IH … Hg HLK2) -L2 -Hg /3 width=3 by drops_drop, ex2_intro/
+ ]
+]
+qed-.