--- /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 "basic_2/grammar/aarity.ma".
+include "basic_2/substitution/ldrop.ma".
+
+(* ATONIC ARITY ASSIGNMENT ON TERMS *****************************************)
+
+inductive aaa: lenv → term → predicate aarity ≝
+| aaa_sort: ∀L,k. aaa L (⋆k) ⓪
+| aaa_lref: ∀I,L,K,V,B,i. ⇩[0, i] L ≡ K. ⓑ{I} V → aaa K V B → aaa L (#i) B
+| aaa_abbr: ∀a,L,V,T,B,A.
+ aaa L V B → aaa (L. ⓓV) T A → aaa L (ⓓ{a}V. T) A
+| aaa_abst: ∀a,L,V,T,B,A.
+ aaa L V B → aaa (L. ⓛV) T A → aaa L (ⓛ{a}V. T) (②B. A)
+| aaa_appl: ∀L,V,T,B,A. aaa L V B → aaa L T (②B. A) → aaa L (ⓐV. T) A
+| aaa_cast: ∀L,V,T,A. aaa L V A → aaa L T A → aaa L (ⓝV. T) A
+.
+
+interpretation "atomic arity assignment (term)"
+ 'AtomicArity L T A = (aaa L T A).
+
+(* Basic inversion lemmas ***************************************************)
+
+fact aaa_inv_sort_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀k. T = ⋆k → A = ⓪.
+#L #T #A * -L -T -A
+[ //
+| #I #L #K #V #B #i #_ #_ #k #H destruct
+| #a #L #V #T #B #A #_ #_ #k #H destruct
+| #a #L #V #T #B #A #_ #_ #k #H destruct
+| #L #V #T #B #A #_ #_ #k #H destruct
+| #L #V #T #A #_ #_ #k #H destruct
+]
+qed.
+
+lemma aaa_inv_sort: ∀L,A,k. L ⊢ ⋆k ⁝ A → A = ⓪.
+/2 width=5/ qed-.
+
+fact aaa_inv_lref_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀i. T = #i →
+ ∃∃I,K,V. ⇩[0, i] L ≡ K. ⓑ{I} V & K ⊢ V ⁝ A.
+#L #T #A * -L -T -A
+[ #L #k #i #H destruct
+| #I #L #K #V #B #j #HLK #HB #i #H destruct /2 width=5/
+| #a #L #V #T #B #A #_ #_ #i #H destruct
+| #a #L #V #T #B #A #_ #_ #i #H destruct
+| #L #V #T #B #A #_ #_ #i #H destruct
+| #L #V #T #A #_ #_ #i #H destruct
+]
+qed.
+
+lemma aaa_inv_lref: ∀L,A,i. L ⊢ #i ⁝ A →
+ ∃∃I,K,V. ⇩[0, i] L ≡ K. ⓑ{I} V & K ⊢ V ⁝ A.
+/2 width=3/ qed-.
+
+fact aaa_inv_abbr_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀a,W,U. T = ⓓ{a}W. U →
+ ∃∃B. L ⊢ W ⁝ B & L. ⓓW ⊢ U ⁝ A.
+#L #T #A * -L -T -A
+[ #L #k #a #W #U #H destruct
+| #I #L #K #V #B #i #_ #_ #a #W #U #H destruct
+| #b #L #V #T #B #A #HV #HT #a #W #U #H destruct /2 width=2/
+| #b #L #V #T #B #A #_ #_ #a #W #U #H destruct
+| #L #V #T #B #A #_ #_ #a #W #U #H destruct
+| #L #V #T #A #_ #_ #a #W #U #H destruct
+]
+qed.
+
+lemma aaa_inv_abbr: ∀a,L,V,T,A. L ⊢ ⓓ{a}V. T ⁝ A →
+ ∃∃B. L ⊢ V ⁝ B & L. ⓓV ⊢ T ⁝ A.
+/2 width=4/ qed-.
+
+fact aaa_inv_abst_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀a,W,U. T = ⓛ{a}W. U →
+ ∃∃B1,B2. L ⊢ W ⁝ B1 & L. ⓛW ⊢ U ⁝ B2 & A = ②B1. B2.
+#L #T #A * -L -T -A
+[ #L #k #a #W #U #H destruct
+| #I #L #K #V #B #i #_ #_ #a #W #U #H destruct
+| #b #L #V #T #B #A #_ #_ #a #W #U #H destruct
+| #b #L #V #T #B #A #HV #HT #a #W #U #H destruct /2 width=5/
+| #L #V #T #B #A #_ #_ #a #W #U #H destruct
+| #L #V #T #A #_ #_ #a #W #U #H destruct
+]
+qed.
+
+lemma aaa_inv_abst: ∀a,L,W,T,A. L ⊢ ⓛ{a}W. T ⁝ A →
+ ∃∃B1,B2. L ⊢ W ⁝ B1 & L. ⓛW ⊢ T ⁝ B2 & A = ②B1. B2.
+/2 width=4/ qed-.
+
+fact aaa_inv_appl_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀W,U. T = ⓐW. U →
+ ∃∃B. L ⊢ W ⁝ B & L ⊢ U ⁝ ②B. A.
+#L #T #A * -L -T -A
+[ #L #k #W #U #H destruct
+| #I #L #K #V #B #i #_ #_ #W #U #H destruct
+| #a #L #V #T #B #A #_ #_ #W #U #H destruct
+| #a #L #V #T #B #A #_ #_ #W #U #H destruct
+| #L #V #T #B #A #HV #HT #W #U #H destruct /2 width=3/
+| #L #V #T #A #_ #_ #W #U #H destruct
+]
+qed.
+
+lemma aaa_inv_appl: ∀L,V,T,A. L ⊢ ⓐV. T ⁝ A →
+ ∃∃B. L ⊢ V ⁝ B & L ⊢ T ⁝ ②B. A.
+/2 width=3/ qed-.
+
+fact aaa_inv_cast_aux: ∀L,T,A. L ⊢ T ⁝ A → ∀W,U. T = ⓝW. U →
+ L ⊢ W ⁝ A ∧ L ⊢ U ⁝ A.
+#L #T #A * -L -T -A
+[ #L #k #W #U #H destruct
+| #I #L #K #V #B #i #_ #_ #W #U #H destruct
+| #a #L #V #T #B #A #_ #_ #W #U #H destruct
+| #a #L #V #T #B #A #_ #_ #W #U #H destruct
+| #L #V #T #B #A #_ #_ #W #U #H destruct
+| #L #V #T #A #HV #HT #W #U #H destruct /2 width=1/
+]
+qed.
+
+lemma aaa_inv_cast: ∀L,W,T,A. L ⊢ ⓝW. T ⁝ A →
+ L ⊢ W ⁝ A ∧ L ⊢ T ⁝ A.
+/2 width=3/ qed-.