{α : Type u_1} →
  {β : Type u_2} →
    {cmpα : α → α → Ordering} →
      {cmpβ : β → β → Ordering} →
        (f : α → β) → [Batteries.RBNode.IsMonotone cmpα cmpβ f] → Batteries.RBSet α cmpα → Batteries.RBSet β cmpβ