∀ {α : Type u} {cmp : α → α → Ordering} {β : Type v} {t : Std.DTreeMap.Raw α (fun x => β) cmp} [Std.TransCmp cmp],
  t.WF → ∀ {k : α} {fallback : β}, Std.DTreeMap.Raw.Const.getD (t.erase k) k fallback = fallback