∀ {α : Type u_1} {β : Type u_2} (f : β → α ⊕ β) (b : β) (n : ℕ) (a' : α),
  Stream'.corec' (Computation.Corec.f f) (Sum.inr b) n = some a' →
    Stream'.corec' (Computation.Corec.f f) (Sum.inr b) (n + 1) = some a'