∀ {α : Type u_1} {cmp : α → α → Ordering} {cut : α → Ordering} {x y : α} {t : Batteries.RBSet α cmp} [Std.TransCmp cmp]
  [Batteries.RBNode.IsStrictCut cmp cut],
  t.upperBoundP? cut = some x → y ∈ t → (cmp y x = Ordering.lt ↔ cut y = Ordering.gt)