∀ {α : Type u_1} {β : Type u_2} (motive : α ⊕ β → Sort u_3) (x : α ⊕ β) (h_1 : (a : α) → motive (Sum.inl a))
  (h_2 : (val : β) → motive (Sum.inr val)) (a : α),
  x = Sum.inl a →
    (match x with
      | Sum.inl a => h_1 a
      | Sum.inr val => h_2 val) ≍
      h_1 a