AN EXPLICIT BASIS FOR RULES ADMISSIBLE IN MODAL SYSTEM S4
Vladimir Vladimirovich Rybakov · 1999
We flnd an explicit basis for all admissible rules of the modal logic S4. Our basis consists of an inflnite sequence of rules which have compact and easy readable form and depend on increasing set of variables. This gives a basis for all quasiidentities valid in the free modal algebra FS4(!) of countable rank.