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