Monodic temporal resolution

TL;DR

This paper extends a resolution technique to monodic fragments of First-Order Temporal Logic, enabling practical proof methods and deepening theoretical understanding of these fragments, especially with expanding domains.

Contribution

It develops a complete resolution calculus for monodic FOTL, facilitating proof procedures and theoretical insights into decidable classes and domain expansions.

Findings

Complete resolution calculus for monodic FOTL

Decidable classes of monodic FOTL identified

Resolution completeness for expanding domains

Abstract

Until recently, First-Order Temporal Logic (FOTL) has been little understood. While it is well known that the full logic has no finite axiomatisation, a more detailed analysis of fragments of the logic was not previously available. However, a breakthrough by Hodkinson et.al., identifying a finitely axiomatisable fragment, termed the monodic fragment, has led to improved understanding of FOTL. Yet, in order to utilise these theoretical advances, it is important to have appropriate proof techniques for the monodic fragment. In this paper, we modify and extend the clausal temporal resolution technique, originally developed for propositional temporal logics, to enable its use in such monodic fragments. We develop a specific normal form for formulae in FOTL, and provide a complete resolution calculus for formulae in this form. Not only is this clausal resolution technique useful as a practical proof technique for certain monodic classes, but the use of this approach provides us with increased understanding of the monodic fragment. In particular, we here show how several features of monodic FOTL are established as corollaries of the completeness result for the clausal temporal resolution method. These include definitions of new decidable monodic classes, simplification of existing monodic classes by reductions, and completeness of clausal temporal resolution in the case of monodic logics with expanding domains, a case with much significance in both theory and practice.