--- /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_2A/reduction/crx.ma".
+include "basic_2A/reduction/cnx.ma".
+
+(* NORMAL TERMS FOR CONTEXT-SENSITIVE EXTENDED REDUCTION ********************)
+
+(* Advanced inversion lemmas on reducibility ********************************)
+
+(* Note: this property is unusual *)
+lemma cnx_inv_crx: ∀h,g,G,L,T. ⦃G, L⦄ ⊢ ➡[h, g] 𝐑⦃T⦄ → ⦃G, L⦄ ⊢ ➡[h, g] 𝐍⦃T⦄ → ⊥.
+#h #g #G #L #T #H elim H -L -T
+[ #L #k #d #Hkd #H
+ lapply (cnx_inv_sort … H) -H #H
+ lapply (deg_mono … H Hkd) -h -L -k <plus_n_Sm #H destruct
+| #I #L #K #V #i #HLK #H
+ elim (cnx_inv_delta … HLK H)
+| #L #V #T #_ #IHV #H
+ elim (cnx_inv_appl … H) -H /2 width=1 by/
+| #L #V #T #_ #IHT #H
+ elim (cnx_inv_appl … H) -H /2 width=1 by/
+| #I #L #V #T * #H1 #H2 destruct
+ [ elim (cnx_inv_zeta … H2)
+ | elim (cnx_inv_eps … H2)
+ ]
+|6,7: #a * [ elim a ] #L #V #T * #H1 #_ #IH #H2 destruct
+ [1,3: elim (cnx_inv_abbr … H2) -H2 /2 width=1 by/
+ |*: elim (cnx_inv_abst … H2) -H2 /2 width=1 by/
+ ]
+| #a #L #V #W #T #H
+ elim (cnx_inv_appl … H) -H #_ #_ #H
+ elim (simple_inv_bind … H)
+| #a #L #V #W #T #H
+ elim (cnx_inv_appl … H) -H #_ #_ #H
+ elim (simple_inv_bind … H)
+]
+qed-.