∀ {α : Type u} {instOrd : Ord α} [Std.TransOrd α] {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β},
  t.WF →
    ∀ {k k' : α} {f : β → β},
      Std.DTreeMap.Internal.Impl.Const.get? (Std.DTreeMap.Internal.Impl.Const.modify k f t) k' =
        if compare k k' = Ordering.eq then Option.map f (Std.DTreeMap.Internal.Impl.Const.get? t k)
        else Std.DTreeMap.Internal.Impl.Const.get? t k'