A deductive-reductive form of logic: Intuitionistic S4 modalities

Abstract

The paper is a continuation of A deductive-reductive form of logic: general theory and intuitionistic case ([1]) and considers the problem of definability of modal operators on the intuitionistic base. Contrary to the classical case, it seems that the fact whether the connective is Heyting’s or Brouwerian is essential for the intuitionistic logic. The connective of possibility has the classical interpretation, if it is defined on the base of the logic with Brouwerian connective of coimplication.