∀ {α : Type u_1} {β : α → Type u_2} [inst : Ord α] [Std.TransOrd α] {t : Std.DTreeMap.Internal.Impl α β}
  {t_ord : t.Ordered} {lowerBound : α},
  (Std.DTreeMap.Internal.rciIterator t lowerBound).toList =
    List.filter (fun e => (compare e.fst lowerBound).isGE) t.toList