-(* Basic_2A1: was: llpx_sn_inv_lift_O *)
-lemma lfxs_inv_lifts_bi: ∀R,L1,L2,U. L1 ⪤*[R, U] L2 →
- ∀K1,K2,i. ⬇*[i] L1 ≡ K1 → ⬇*[i] L2 ≡ K2 →
- ∀T. ⬆*[i] T ≡ U → K1 ⪤*[R, T] K2.
-#R #L1 #L2 #U #HL12 #K1 #K2 #i #HLK1 #HLK2 #T #HTU
+(* Basic_2A1: uses: llpx_sn_inv_lift_O *)
+lemma lfxs_inv_lifts_bi: ∀R,L1,L2,U. L1 ⪤*[R, U] L2 → ∀b,f. 𝐔⦃f⦄ →
+ ∀K1,K2. ⬇*[b, f] L1 ≡ K1 → ⬇*[b, f] L2 ≡ K2 →
+ ∀T. ⬆*[f] T ≡ U → K1 ⪤*[R, T] K2.
+#R #L1 #L2 #U #HL12 #b #f #Hf #K1 #K2 #HLK1 #HLK2 #T #HTU