-axiom cpr_delta: ∀L,K,V0,V,i.
- ↓[0, i] L ≡ K. 𝕓{Abbr} V0 → ↑[0, i + 1] V0 ≡ V → L ⊢ #i ⇒ V.
-(*
-#L #K #V0 #V #i #HLK #HV0
-@ex2_1_intro [2: // |1: skip ]
-@pts_subst [4,6,7,8: // |1,2,3: skip |5:
-*)
+lemma cpr_delta: ∀L,K,V1,V2,V,i.
+ ↓[0, i] L ≡ K. 𝕓{Abbr} V1 → K ⊢ V1 [0, |L| - i - 1] ≫ V2 →
+ ↑[0, i + 1] V2 ≡ V → L ⊢ #i ⇒ V.
+#L #K #V1 #V2 #V #i #HLK #HV12 #HV2
+@ex2_1_intro [2: // | skip ] /3 width=8/ (**) (* /4/ is too slow *)
+qed.