∀ {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 → ∀ {k : α} {v : β k}, (t.getThenInsertIfNew? k v).1 = t.get? k