∀ {α : Type u} {instOrd : Ord α} {β : Type v} {t : Std.DTreeMap.Internal.Impl α fun x => β} [Std.TransOrd α],
  t.WF →
    ∀ {k k' : α} {f : Option β → Option β},
      (Std.DTreeMap.Internal.Impl.Const.alter! k f t).getKey? k' =
        if compare k k' = Ordering.eq then
          if (f (Std.DTreeMap.Internal.Impl.Const.get? t k)).isSome = true then some k else none
        else t.getKey? k'