+
+(* Basic_1: was just: sn3_abbr *)
+(* Basic_2A1: was: csx_lref_bind *)
+lemma csx_lref_pair: ∀h,o,I,G,L,K,V,i. ⬇*[i] L ≘ K.ⓑ{I}V →
+ ⦃G, K⦄ ⊢ ⬈*[h, o] 𝐒⦃V⦄ → ⦃G, L⦄ ⊢ ⬈*[h, o] 𝐒⦃#i⦄.
+#h #o #I #G #L #K #V #i #HLK #HV
+@csx_intro #X #H #Hi elim (cpx_inv_lref1_drops … H) -H
+[ #H destruct elim Hi //
+| -Hi * #I0 #K0 #V0 #V1 #HLK0 #HV01 #HV1
+ lapply (drops_mono … HLK0 … HLK) -HLK #H destruct
+ /3 width=8 by csx_lifts, csx_cpx_trans, drops_isuni_fwd_drop2/
+]
+qed.
+
+(* Advanced inversion lemmas ************************************************)
+
+(* Basic_1: was: sn3_gen_def *)
+(* Basic_2A1: was: csx_inv_lref_bind *)
+lemma csx_inv_lref_pair: ∀h,o,I,G,L,K,V,i. ⬇*[i] L ≘ K.ⓑ{I}V →
+ ⦃G, L⦄ ⊢ ⬈*[h, o] 𝐒⦃#i⦄ → ⦃G, K⦄ ⊢ ⬈*[h, o] 𝐒⦃V⦄.
+#h #o #I #G #L #K #V #i #HLK #Hi
+elim (lifts_total V (𝐔❴↑i❵))
+/4 width=9 by csx_inv_lifts, csx_cpx_trans, cpx_delta_drops, drops_isuni_fwd_drop2/
+qed-.
+
+lemma csx_inv_lref: ∀h,o,G,L,i. ⦃G, L⦄ ⊢ ⬈*[h, o] 𝐒⦃#i⦄ →
+ ∨∨ ⬇*[Ⓕ, 𝐔❴i❵] L ≘ ⋆
+ | ∃∃I,K. ⬇*[i] L ≘ K.ⓤ{I}
+ | ∃∃I,K,V. ⬇*[i] L ≘ K.ⓑ{I}V & ⦃G, K⦄ ⊢ ⬈*[h, o] 𝐒⦃V⦄.
+#h #o #G #L #i #H elim (drops_F_uni L i) /2 width=1 by or3_intro0/
+* * /4 width=9 by csx_inv_lref_pair, ex2_3_intro, ex1_2_intro, or3_intro2, or3_intro1/
+qed-.