- degree-based equivalene for terms

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

diff --git a/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/fpa/fpa.etc b/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/fpa/fpa.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                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "basic_2/notation/relations/rajust_5.ma".
+include "basic_2/substitution/drop.ma".
+
+(* AJUSTMENT ****************************************************************)
+
+inductive fpa (s:bool): bi_relation lenv term ≝
+| fpa_fwd: ∀L,K,T,U,d,e. ⇩[s, d, e] L ≡ K → ⇧[d, e] T ≡ U → fpa s K T L U
+| fpa_bwd: ∀L,K,T,U,d,e. ⇩[s, d, e] L ≡ K → ⇧[d, e] T ≡ U → fpa s L U K T
+.
+
+interpretation
+   "ajustment (restricted closure)"
+   'RAjust L1 T1 s L2 T2 = (fpa s L1 T1 L2 T2).
+
+(* Basic properties *********************************************************)
+
+lemma fpa_refl: ∀s. bi_reflexive … (fpa s).
+/2 width=4 by fpa_fwd/ qed.
+
+lemma fpa_sym: ∀s. bi_symmetric … (fpa s).
+#s #L1 #L2 #T1 #T2 * /2 width=4 by fpa_fwd, fpa_bwd/
+qed-.