- (Y1 = ⋆ ∧ Y2 = ⋆) ∨
- ∃∃I,L1,L2,V1,V2. L1 ⪤*[R, V1] L2 & R L1 V1 V2 &
- Y1 = L1.ⓑ{I}V1 & Y2 = L2.ⓑ{I}V2.
-#R #Y1 #Y2 * #f #H1 #H2 elim (frees_inv_zero … H1) -H1 *
-[ #H #_ lapply (lexs_inv_atom1_aux … H2 H) -H2 /3 width=1 by or_introl, conj/
-| #I1 #L1 #V1 #g #HV1 #HY1 #Hg elim (lexs_inv_next1_aux … H2 … HY1 Hg) -H2 -Hg
- /4 width=9 by ex4_5_intro, ex2_intro, or_intror/
+ ∨∨ Y1 = ⋆ ∧ Y2 = ⋆
+ | ∃∃I,L1,L2,V1,V2. L1 ⪤*[R, V1] L2 & R L1 V1 V2 &
+ Y1 = L1.ⓑ{I}V1 & Y2 = L2.ⓑ{I}V2
+ | ∃∃f,I,L1,L2. 𝐈⦃f⦄ & L1 ⪤*[cext2 R, cfull, f] L2 &
+ Y1 = L1.ⓤ{I} & Y2 = L2.ⓤ{I}.
+#R * [ | #Y1 * #I1 [ | #X ] ] #Y2 * #f #H1 #H2
+[ lapply (lexs_inv_atom1 … H2) -H2 /3 width=1 by or3_intro0, conj/
+| elim (frees_inv_unit … H1) -H1 #g #HX #H destruct
+ elim (lexs_inv_next1 … H2) -H2 #I2 #L2 #HL12 #H #H2 destruct
+ >(ext2_inv_unit_sn … H) -H /3 width=8 by or3_intro2, ex4_4_intro/
+| elim (frees_inv_pair … H1) -H1 #g #Hg #H destruct
+ elim (lexs_inv_next1 … H2) -H2 #Z2 #L2 #HL12 #H
+ elim (ext2_inv_pair_sn … H) -H
+ /4 width=9 by or3_intro1, ex4_5_intro, ex2_intro/