The Limits of Tractability in Resolution-Based Propositional Proof Systems

We study classes of propositional contradictions based on the Least Number Principle (LNP) in the refutation system of Resolution and its generalisations with bounded conjunction, Res(k). We prove that any first-order sentence with no finite models that admits a 1 interpretation of the LNP, relativised to a set that is quantifier-free definable, generates a sequence of propositional contradictions that have polynomially-sized refutations in the system Res(k), for some k. When one considers the LNP with total order we demonstrate that a 1 interpretation of this is sufficient to generate such a propositional sequence with polynomially-sized refutations in the system Res(k). On the other hand, we prove that a very simple first-order sentence that admits a 1 interpretation of the LNP (with partial and not total order) requires exponentially-sized refutations in Resolution.

• Type: Conference
• Year: 2010
• Where: CIE
• Authors: Stefan S. Dantchev, Barnaby Martin
• Keywords: Applied Computing, CIE 2010, Least Number Principle, Propositional Contradictions, Refutations