∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [Std.TransOrd α]
  [inst : Inhabited β],
  t.WF →
    ∀ {a : α}, Std.DTreeMap.Internal.Impl.contains a t = false → Std.DTreeMap.Internal.Impl.Const.get! t a = default