Effective Completeness for S4.3.1-Theories with Respect to Discrete Linear Models

Abstract: The computable model theory of modal logic was initiated by Suman Ganguli and Anil Nerode in [4]. They use an effective Henkin-type construction to effectivize various completeness theorems from classical modal logic. This construction has the feature of only producing models whose frames can be obtained by adding edges to a tree digraph. Consequently, this construction cannot prove an effective version of a well-known completeness theorem which states that every $\mathsf{S4.3.1}$-theory has a model whose accessibility relation is a linear order of order type $\omega$. We prove an effectivization of that theorem by means of a new construction adapted from that of Ganguli and Nerode.