Canonical Logic Programs are Succinctly Incomparable with Propositional Formulas

Canonical (logic) programs (CP) refer to normal logic programs augmented with connective not not. In this paper we address the question of whether CP are succinctly incomparable with propositional formulas (PF). Our main result shows that the PARITY problem, which can be polynomially represented in PF but only has exponential representations in CP. In other words, PARITY separates PF from CP. Simply speaking, this means that exponential size blowup is generally inevitable when translating a set of formulas in PF into an equivalent program in CP (without introducing new variables). Furthermore, since it has been shown by Lifschitz and Razborov that there is also a problem that separates CP from PF (assuming P * NC/poly), it follows that CP and PF are indeed succinctly incomparable. From the view of the theory of computation, the above result may also be considered as the separation of two models of computation, i.e., we identify a language in NC/poly which is not in the set of languages computable by polynomial size CP programs.