∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [Std.TransOrd α],
  t.WF →
    ∀ {k a : α} {v : β},
      Std.DTreeMap.Internal.Impl.Const.get? (Std.DTreeMap.Internal.Impl.insertIfNew! k v t) a =
        if compare k a = Ordering.eq ∧ k ∉ t then some v else Std.DTreeMap.Internal.Impl.Const.get? t a