-(* Note: the constant 0 cannot be generalized *)
-lemma lsuba_drop_O1_conf: ∀G,L1,L2. G ⊢ L1 ⫃⁝ L2 → ∀K1,c,k. ⬇[c, 0, k] L1 ≡ K1 →
- ∃∃K2. G ⊢ K1 ⫃⁝ K2 & ⬇[c, 0, k] L2 ≡ K2.
+(* Note: the premise 𝐔⦃f⦄ cannot be removed *)
+(* Basic_2A1: includes: lsuba_drop_O1_conf *)
+lemma lsuba_drops_conf_isuni: ∀G,L1,L2. G ⊢ L1 ⫃⁝ L2 →
+ ∀K1,c,f. 𝐔⦃f⦄ → ⬇*[c, f] L1 ≡ K1 →
+ ∃∃K2. G ⊢ K1 ⫃⁝ K2 & ⬇*[c, f] L2 ≡ K2.