∀ {α : Type u} {cmp : α → α → Ordering} [Std.TransCmp cmp] {β : Type v} {t : Std.DTreeMap.Raw α (fun x => β) cmp},
  t.WF →
    ∀ [inst : Inhabited α] {k k' : α} {f : β → β},
      (Std.DTreeMap.Raw.Const.modify t k f).getKey! k' =
        if cmp k k' = Ordering.eq then if k ∈ t then k else default else t.getKey! k'