Unification in pretabular extensions of S4

Abstract

L.L. Maksimova and L. Esakia, V. Meskhi showed that the modal logic S4 has exactly 5 pretabular extensions: PM1-PM5. In this paper, we study and systematize the problem of unification for all given pretabular logics. We showed that PM2,PM3 have finitary, and PM1,PM4,PM5 have unitary types of unification. Complete sets of unifiers in logics are described.