∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [Std.TransOrd α]
  [inst : BEq α] [Std.LawfulBEqOrd α] (h : t.WF) {l : List (α × β)} {k : α},
  Std.DTreeMap.Internal.Impl.contains k ↑(Std.DTreeMap.Internal.Impl.Const.insertMany t l ⋯) = true →
    List.findSomeRev?
          (fun x =>
            match x with
            | (a, b) => if compare a k = Ordering.eq then some b else none)
          l =
        none →
      Std.DTreeMap.Internal.Impl.contains k t = true