rfl
case refl.e_val.e_val.e_a.right
n : Nat
ih :
  ∀ (p : Fin n → Prop) [inst : DecidablePred p] (k : Fin (count p)) (i : { i // p i }),
    decodeSubtype p k = i ↔ encodeSubtype p i = k
p : Fin (n + 1) → Prop
inst : DecidablePred p
k : Fin (count p)
i✝ : { i // p i }
h0 : p 0
this✝ : count p = (count fun i => p i.succ) + 1
k✝ : Nat
hk✝ : k✝ < count p
k' : Nat
hk' : k' + 1 < count p
i : Nat
hi : i + 1 < n + 1
hp : p ⟨i + 1, hi⟩
hk : k'.succ < count p
h : encodeSubtype p ⟨⟨i + 1, hi⟩, hp⟩ = ⟨k'.succ, hk⟩
heq✝ : ⋯ ≅ hk'
this : decodeSubtype (fun i => p i.succ) ⟨k', ⋯⟩ = ⟨⟨i, ⋯⟩, hp⟩
⊢ ↑⟨⟨i, ⋯⟩, hp⟩.val = i
no goals