Satisfiability Checking in Łukasiewicz Logic as Finite Constraint Satisfaction.

Abstract Although it is well-known that every satisfiable formula in Łukasiewicz’ infinite-valued logic \(\mathcal{L}_{\infty}\) can be satisfied in some finite-valued logic, practical methods for finding an appropriate number of truth degrees do currently not exist. Extending upon earlier results by Aguzzoli et al., which only take the total number of variable occurrences into account, we present a detailed analysis of what type of formulas require a large number of truth degrees to be satisfied. In particular, we reveal important links between this number of truth degrees and the dimension, and structure, of the cycle space of an associated bipartite graph. We furthermore propose an efficient, polynomial-time algorithm for establishing a strong upper bound on the required number of truth degrees, allowing us to check the satisfiability of sets of formulas in \(\mathcal{L}_{\infty}\), and more generally, sets of fuzzy clauses over Łukasiewicz logic formulas, by solving a small number of constraint satisfaction problems. In an experimental evaluation, we demonstrate the practical usefulness of this approach, comparing it with a state-of-the-art technique based on mixed integer programming.