- degree-based equivalene for terms

[helm.git] / matita / matita / contribs / lambdadelta / basic_2 / etc_2A1 / lsubr / lsubr.etc

diff --git a/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/lsubr/lsubr.etc b/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/lsubr/lsubr.etc
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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                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+notation "hvbox( L1 ⓝ ⊑ break term 46 L2 )"
+   non associative with precedence 45
+   for @{ 'LRSubEqT $L1 $L2 }.
+
+include "basic_2/relocation/ldrop.ma".
+
+(* LOCAL ENVIRONMENT REFINEMENT FOR SUBSTITUTION ****************************)
+
+inductive lsubr: relation lenv ≝
+| lsubr_sort: ∀L. lsubr L (⋆)
+| lsubr_abbr: ∀L1,L2,V. lsubr L1 L2 → lsubr (L1. ⓓV) (L2.ⓓV)
+| lsubr_abst: ∀I,L1,L2,V1,V2. lsubr L1 L2 → lsubr (L1. ⓑ{I}V1) (L2. ⓛV2)
+.
+
+interpretation
+  "local environment refinement (substitution)"
+  'CrSubEq L1 L2 = (lsubr L1 L2).
+
+(* Basic properties *********************************************************)
+
+lemma lsubr_bind: ∀I,L1,L2,V. L1 ⊑ L2 → L1. ⓑ{I} V ⊑ L2.ⓑ{I} V.
+* /2 width=1/ qed.
+
+lemma lsubr_abbr: ∀I,L1,L2,V. L1 ⊑ L2 → L1. ⓓV ⊑ L2. ⓑ{I}V.
+* /2 width=1/ qed.
+
+lemma lsubr_refl: ∀L. L ⊑ L.
+#L elim L -L // /2 width=1/
+qed.
+
+(* Basic inversion lemmas ***************************************************)
+
+fact lsubr_inv_atom1_aux: ∀L1,L2. L1 ⊑ L2 → L1 = ⋆ → L2 = ⋆.
+#L1 #L2 * -L1 -L2 //
+[ #L1 #L2 #V #_ #H destruct
+| #I #L1 #L2 #V1 #V2 #_ #H destruct
+]
+qed-.
+
+lemma lsubr_inv_atom1: ∀L2. ⋆ ⊑ L2 → L2 = ⋆.
+/2 width=3 by lsubr_inv_atom1_aux/ qed-.
+
+fact lsubr_inv_abbr2_aux: ∀L1,L2. L1 ⊑ L2 → ∀K2,W. L2 = K2.ⓓW →
+                          ∃∃K1. K1 ⊑ K2 & L1 = K1.ⓓW.
+#L1 #L2 * -L1 -L2
+[ #L #K2 #W #H destruct
+| #L1 #L2 #V #HL12 #K2 #W #H destruct /2 width=3/
+| #I #L1 #L2 #V1 #V2 #_ #K2 #W #H destruct
+]
+qed-.
+
+lemma lsubr_inv_abbr2: ∀L1,K2,W. L1 ⊑ K2.ⓓW →
+                       ∃∃K1. K1 ⊑ K2 & L1 = K1.ⓓW.
+/2 width=3 by lsubr_inv_abbr2_aux/ qed-.
+
+fact lsubr_inv_abst2_aux: ∀L1,L2. L1 ⊑ L2 → ∀K2,W2. L2 = K2.ⓛW2 →
+                          ∃∃I,K1,W1. K1 ⊑ K2 & L1 = K1.ⓑ{I}W1.
+#L1 #L2 * -L1 -L2
+[ #L #K2 #W2 #H destruct
+| #L1 #L2 #V #_ #K2 #W2 #H destruct
+| #I #L1 #L2 #V1 #V2 #HL12 #K2 #W2 #H destruct /2 width=5/
+]
+qed-.
+
+lemma lsubr_inv_abst2: ∀L1,K2,W2. L1 ⊑ K2.ⓛW2 →
+                       ∃∃I,K1,W1. K1 ⊑ K2 & L1 = K1.ⓑ{I}W1.
+/2 width=4 by lsubr_inv_abst2_aux/ qed-.
+
+(* Basic forward lemmas *****************************************************)
+
+lemma lsubr_fwd_length: ∀L1,L2. L1 ⊑ L2 → |L2| ≤ |L1|.
+#L1 #L2 #H elim H -L1 -L2 // /2 width=1/
+qed-.
+
+lemma lsubr_fwd_ldrop2_abbr: ∀L1,L2. L1 ⊑ L2 →
+                             ∀K2,W,i. ⇩[0, i] L2 ≡ K2. ⓓW →
+                             ∃∃K1. K1 ⊑ K2 & ⇩[0, i] L1 ≡ K1. ⓓW.
+#L1 #L2 #H elim H -L1 -L2
+[ #L #K2 #W #i #H
+  elim (ldrop_inv_atom1 … H) -H #H destruct
+| #L1 #L2 #V #HL12 #IHL12 #K2 #W #i #H
+  elim (ldrop_inv_O1_pair1 … H) -H * #Hi #HLK2 destruct [ -IHL12 | -HL12 ]
+  [ /2 width=3/
+  | elim (IHL12 … HLK2) -IHL12 -HLK2 /3 width=3/
+  ]
+| #I #L1 #L2 #V1 #V2 #_ #IHL12 #K2 #W #i #H
+  elim (ldrop_inv_O1_pair1 … H) -H * #Hi #HLK2 destruct
+  elim (IHL12 … HLK2) -IHL12 -HLK2 /3 width=3/
+]
+qed-.