The Role of Decidability in First Order Separations over Classes of Finite Structures


We establish that the decidability of the first order theory of a class of finite structures is a simple and useful condition for guaranteeing that the expressive power of FO + LFP properly extends that of FO on , unifying separation results for various classes of structures that have been studied. We then apply this result to show that it encompasses… (More)
DOI: 10.1109/LICS.2000.855754