 Stavi later proposed two more operators, \(S^{\prime}\) and \(U^{\prime},\) which, when added to \(S\) and \(U\), make the temporal language expressively complete on all linear frames. Yet, as shown by Gabbay, no finite number of new operators can make the temporal language functionally complete on all partial orderings. See Gabbay et al. (1994) for an overview of these results.