∀ {α : Type u} {a : α} {motive : (a_1 : List α) → List.Mem a a_1 → Prop} {a_1 : List α} (t : List.Mem a a_1),
  (∀ (as : List α), motive (a :: as) ⋯) →
    (∀ (b : α) {as : List α} (a_2 : List.Mem a as), motive (b :: as) ⋯) → motive a_1 t