Several characterizations of the 4–valued modal algebras

摘要

A. Monteiro, in 1978, defined the algebras he named tetravalent modal algebras,? that will be called? {em $4-$valued modal algebras} in this work. These algebras constitute a generalization of the $3-$valued Lukasiewicz algebras defined by Moisil. The theory of the $4-$valued modal algebras has been widely developed by I. Loureiro in cite{IL1, IL2, IL3, IL4, IL5, IL6, IL7} and by A. V. Figallo in cite{FI3, FI4, AF.PL,AF.AZ}. J. Font and M. Rius indicated, in the introduction to the important work cite{JF.MR2}, a brief but detailed review on the $4-$valued modal algebras. In this work varied characterizations are presented that show the ``closeness'' this variety of algebras has with other well--known algebras related to the algebraic counterparts of certain logics.