∀ {ε α : Type u_1} (motive : Except ε α → Sort u_2) (a : α) (h_1 : (a : α) → motive (Except.ok a))
  (h_2 : (e : ε) → motive (Except.error e)),
  (match Except.ok a with
    | Except.ok a => h_1 a
    | Except.error e => h_2 e) =
    h_1 a