∀ {α : Type u_1} {cmp : α → α → Ordering} {y : α} {t : Batteries.RBSet α cmp}
  (motive : (∃ y_1 ∈ t.toList, cmp y y_1 = Ordering.eq) → Prop) (x : ∃ y_1 ∈ t.toList, cmp y y_1 = Ordering.eq),
  (∀ (w : α) (h1 : w ∈ t.toList) (h2 : cmp y w = Ordering.eq), motive ⋯) → motive x