refine Nat.recAscend (motive:=λ i => ∀ acc, Array.ofFn.go f i acc = acc ++ Array.ofFn.go f i #[]) (n:=n) ?_ ?_ i (Nat.le_of_lt hlt) acc
α✝ α : Type u
n : Nat
f : Fin n → α
i : Nat
acc : Array α
hlt : i < n
⊢ ofFn.go f i acc = acc ++ ofFn.go f i #[]
case refine_1
α✝ α : Type u
n : Nat
f : Fin n → α
i : Nat
acc : Array α
hlt : i < n
⊢ (fun i => ∀ (acc : Array α), ofFn.go f i acc = acc ++ ofFn.go f i #[]) n

case refine_2
α✝ α : Type u
n : Nat
f : Fin n → α
i : Nat
acc : Array α
hlt : i < n
⊢ ∀ (k : Nat),
    k < n →
      (fun i => ∀ (acc : Array α), ofFn.go f i acc = acc ++ ofFn.go f i #[]) (Nat.succ k) →
        (fun i => ∀ (acc : Array α), ofFn.go f i acc = acc ++ ofFn.go f i #[]) k