∀ {α : Type u} {n : ℕ} (f f_1 : Fin n → α),
  f = f_1 →
    ∀ (acc acc_1 : Array α),
      acc = acc_1 →
        ∀ (i i_1 : ℕ) (e_i : i = i_1) (a : i ≤ n), Array.ofFn.go✝ f acc i a = Array.ofFn.go✝¹ f_1 acc_1 i_1 ⋯