∀ {α : Type u} {cmp : α → α → Ordering} [Std.TransCmp cmp] {β : Type v} {t : Std.DTreeMap.Raw α (fun x => β) cmp},
  t.WF →
    ∀ {k : α} {f : β → β},
      Std.DTreeMap.Raw.Const.get? (Std.DTreeMap.Raw.Const.modify t k f) k =
        Option.map f (Std.DTreeMap.Raw.Const.get? t k)