∀ {α : Type u_1} {β : Type u_2} {p : α ⊕ β → Prop}
  (motive : ((∀ (a : α), p (Sum.inl a)) ∧ ∀ (b : β), p (Sum.inr b)) → Prop)
  (x : (∀ (a : α), p (Sum.inl a)) ∧ ∀ (b : β), p (Sum.inr b)),
  (∀ (h₁ : ∀ (a : α), p (Sum.inl a)) (h₂ : ∀ (b : β), p (Sum.inr b)), motive ⋯) → motive x