+
+lemma ntas_refl (h) (a) (G) (L):
+ ∀T. ⦃G,L⦄ ⊢ T ![h,a] → ⦃G,L⦄ ⊢ T :*[h,a,0] T.
+/2 width=3 by ntas_intro/ qed.
+
+lemma ntas_sort (h) (a) (n) (G) (L):
+ ∀s. ⦃G,L⦄ ⊢ ⋆s :*[h,a,n] ⋆((next h)^n s).
+#h #a #n #G #L #s
+/2 width=3 by ntas_intro, cnv_sort, cpms_sort/
+qed.
+
+lemma ntas_bind_cnv (h) (a) (n) (G) (K):
+ ∀V. ⦃G,K⦄ ⊢ V ![h,a] →
+ ∀I,T,U. ⦃G,K.ⓑ{I}V⦄ ⊢ T :*[h,a,n] U →
+ ∀p. ⦃G,K⦄ ⊢ ⓑ{p,I}V.T :*[h,a,n] ⓑ{p,I}V.U.
+#h #a #n #G #K #V #HV #I #T #U
+* #X #HU #HT #HUX #HTX #p
+/3 width=5 by ntas_intro, cnv_bind, cpms_bind_dx/
+qed.
+
+(* Basic_forward lemmas *****************************************************)
+
+lemma ntas_fwd_cnv_sn (h) (a) (n) (G) (L):
+ ∀T,U. ⦃G,L⦄ ⊢ T :*[h,a,n] U → ⦃G,L⦄ ⊢ T ![h,a].
+#h #a #n #G #L #T #U
+* #X #_ #HT #_ #_ //
+qed-.
+
+(* Note: this is ntas_fwd_correct_cnv *)
+lemma ntas_fwd_cnv_dx (h) (a) (n) (G) (L):
+ ∀T,U. ⦃G,L⦄ ⊢ T :*[h,a,n] U → ⦃G,L⦄ ⊢ U ![h,a].
+#h #a #n #G #L #T #U
+* #X #HU #_ #_ #_ //
+qed-.