∀ {α : Type u} {cmp : α → α → Ordering} {β : Type v} {t : Std.DTreeMap.Raw α (fun x => β) cmp} [Std.TransCmp cmp]
  [Inhabited α],
  t.WF →
    ∀ {k fallback : α} {f : Option β → Option β},
      (Std.DTreeMap.Raw.Const.alter t k f).getKeyD k fallback =
        if (f (Std.DTreeMap.Raw.Const.get? t k)).isSome = true then k else fallback