change (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).fst = f
t : Th
Δ : Ctx
f : Form
i j : ℕ
prf₃ : BProof (lindenbaumSequence t Δ (i + 1, Encodable.encode (f, f))) (f¦f)
prev : Ctx := lindenbaumSequence t Δ (i + 1, Encodable.encode (f, f))
l : Form := (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).fst
r : Form := (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).snd
⊢ l = f
t : Th
Δ : Ctx
f : Form
i j : ℕ
prf₃ : BProof (lindenbaumSequence t Δ (i + 1, Encodable.encode (f, f))) (f¦f)
prev : Ctx := lindenbaumSequence t Δ (i + 1, Encodable.encode (f, f))
l : Form := (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).fst
r : Form := (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).snd
⊢ (Denumerable.ofNat (Form × Form) (Encodable.encode (f, f))).fst = f