rfl
case a.left.h.refl
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
k : Nat
hk : k < count p
hi : ↑(decodeSubtype (fun i => p i.succ) ⟨k, ⋯⟩).1 + 1 < n + 1
hp : p ⟨↑(decodeSubtype (fun i => p i.succ) ⟨k, ⋯⟩).1 + 1, hi⟩
⊢ decodeSubtype (fun i => p i.succ) ⟨k, ⋯⟩ = ⟨⟨↑(decodeSubtype (fun i => p i.succ) ⟨k, ⋯⟩).1, ⋯⟩, hp⟩
no goals