∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.DTreeMap.Raw α β cmp} [Std.TransCmp cmp]
  [inst : Std.LawfulEqCmp cmp],
  t.WF → ∀ [inst_1 : Inhabited α] {k : α} {f : β k → β k}, (t.modify k f).getKey! k = if k ∈ t then k else default