+lemma lsubf_beta_tl_dx: ∀f,f0,g1,L1,V. L1 ⊢ 𝐅*⦃V⦄ ≘ f → f0 ⋓ f ≘ g1 →
+ ∀f2,L2,W. ⦃L1, f0⦄ ⫃𝐅* ⦃L2, ⫱f2⦄ →
+ ∃∃f1. ⦃L1.ⓓⓝW.V, f1⦄ ⫃𝐅* ⦃L2.ⓛW, f2⦄ & ⫱f1 ⊆ g1.
+#f #f0 #g1 #L1 #V #Hf #Hg1 #f2
+elim (pn_split f2) * #x2 #H2 #L2 #W #HL12 destruct
+[ /3 width=4 by lsubf_push, sor_inv_sle_sn, ex2_intro/
+| @(ex2_intro … (↑g1)) /2 width=5 by lsubf_beta/ (**) (* full auto fails *)
+]
+qed-.
+
+(* Note: this might be moved *)
+lemma lsubf_inv_sor_dx: ∀f1,f2,L1,L2. ⦃L1, f1⦄ ⫃𝐅* ⦃L2, f2⦄ →
+ ∀f2l,f2r. f2l⋓f2r ≘ f2 →
+ ∃∃f1l,f1r. ⦃L1, f1l⦄ ⫃𝐅* ⦃L2, f2l⦄ & ⦃L1, f1r⦄ ⫃𝐅* ⦃L2, f2r⦄ & f1l⋓f1r ≘ f1.
+#f1 #f2 #L1 #L2 #H elim H -f1 -f2 -L1 -L2
+[ /3 width=7 by sor_eq_repl_fwd3, ex3_2_intro/
+| #g1 #g2 #I1 #I2 #L1 #L2 #_ #IH #f2l #f2r #H
+ elim (sor_inv_xxp … H) -H [|*: // ] #g2l #g2r #Hg2 #Hl #Hr destruct
+ elim (IH … Hg2) -g2 /3 width=11 by lsubf_push, sor_pp, ex3_2_intro/
+| #g1 #g2 #I #L1 #L2 #_ #IH #f2l #f2r #H
+ elim (sor_inv_xxn … H) -H [1,3,4: * |*: // ] #g2l #g2r #Hg2 #Hl #Hr destruct
+ elim (IH … Hg2) -g2 /3 width=11 by lsubf_push, lsubf_bind, sor_np, sor_pn, sor_nn, ex3_2_intro/
+| #g #g0 #g1 #g2 #L1 #L2 #W #V #Hg #Hg1 #_ #IH #f2l #f2r #H
+ elim (sor_inv_xxn … H) -H [1,3,4: * |*: // ] #g2l #g2r #Hg2 #Hl #Hr destruct
+ elim (IH … Hg2) -g2 #g1l #g1r #Hl #Hr #Hg0
+ [ lapply (sor_comm_23 … Hg0 Hg1 ?) -g0 [3: |*: // ] #Hg1
+ /3 width=11 by lsubf_push, lsubf_beta, sor_np, ex3_2_intro/
+ | lapply (sor_assoc_dx … Hg1 … Hg0 ??) -g0 [3: |*: // ] #Hg1
+ /3 width=11 by lsubf_push, lsubf_beta, sor_pn, ex3_2_intro/
+ | lapply (sor_distr_dx … Hg0 … Hg1) -g0 [5: |*: // ] #Hg1
+ /3 width=11 by lsubf_beta, sor_nn, ex3_2_intro/
+ ]
+| #g #g0 #g1 #g2 #I1 #I2 #L1 #L2 #V #Hg #Hg1 #_ #IH #f2l #f2r #H
+ elim (sor_inv_xxn … H) -H [1,3,4: * |*: // ] #g2l #g2r #Hg2 #Hl #Hr destruct
+ elim (IH … Hg2) -g2 #g1l #g1r #Hl #Hr #Hg0
+ [ lapply (sor_comm_23 … Hg0 Hg1 ?) -g0 [3: |*: // ] #Hg1
+ /3 width=11 by lsubf_push, lsubf_unit, sor_np, ex3_2_intro/
+ | lapply (sor_assoc_dx … Hg1 … Hg0 ??) -g0 [3: |*: // ] #Hg1
+ /3 width=11 by lsubf_push, lsubf_unit, sor_pn, ex3_2_intro/
+ | lapply (sor_distr_dx … Hg0 … Hg1) -g0 [5: |*: // ] #Hg1
+ /3 width=11 by lsubf_unit, sor_nn, ex3_2_intro/
+ ]
+]
+qed-.