Classification of extensions of the modal logic S4
Larisa Lvovna Maksimova · Siberian Mathematical Journal · 2013
We introduce a natural classification of normal extensions of the modal logic S4 in accordance to the volumes of clusters in the Kripke frames and prove the decidability of the classification. We distinguish the main logics in this classification and establish their important properties: finite axiomatizability, finite approximability, and recognizability.