--- /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/substitution/ldrop_ldrop.ma".
+include "basic_2/static/aaa.ma".
+
+(* ATONIC ARITY ASSIGNMENT ON TERMS *****************************************)
+
+(* Main properties **********************************************************)
+
+theorem aaa_mono: ∀L,T,A1. L ⊢ T ⁝ A1 → ∀A2. L ⊢ T ⁝ A2 → A1 = A2.
+#L #T #A1 #H elim H -L -T -A1
+[ #L #k #A2 #H
+ >(aaa_inv_sort … H) -H //
+| #I1 #L #K1 #V1 #B #i #HLK1 #_ #IHA1 #A2 #H
+ elim (aaa_inv_lref … H) -H #I2 #K2 #V2 #HLK2 #HA2
+ lapply (ldrop_mono … HLK1 … HLK2) -L #H destruct /2 width=1/
+| #a #L #V #T #B1 #A1 #_ #_ #_ #IHA1 #A2 #H
+ elim (aaa_inv_abbr … H) -H /2 width=1/
+| #a #L #V1 #T1 #B1 #A1 #_ #_ #IHB1 #IHA1 #X #H
+ elim (aaa_inv_abst … H) -H #B2 #A2 #HB2 #HA2 #H destruct /3 width=1/
+| #L #V1 #T1 #B1 #A1 #_ #_ #_ #IHA1 #A2 #H
+ elim (aaa_inv_appl … H) -H #B2 #_ #HA2
+ lapply (IHA1 … HA2) -L #H destruct //
+| #L #V #T #A1 #_ #_ #_ #IHA1 #A2 #H
+ elim (aaa_inv_cast … H) -H /2 width=1/
+]
+qed-.