Boole's Method I. A Modern Version

A rigorous, modern version of Boole's algebra of logic is presented, based partly on the 1890s treatment of Ernst Schroder

The lattice of varieties of implication semigroups

In 2012, the second author introduced and examined a new type of algebras as a generalization of De Morgan algebras. These algebras are of type (2,0) with one binary and one nullary operation satisfying two certain specific identities. Such algebras are called implication zroupoids. They invesigated in a number of articles by the second author and J.M.Cornejo. In these articles several varieties of implication zroupoids satisfying the associative law appeared. Implication zroupoids satisfying the associative law are called implication semigroups. Here we completely describe the lattice of all varieties of implication semigroups. It turns out that this lattice is non-modular and consists of 16 elements.Comment: Compared with the previous version, we rewrite Section 3 and add Appendixes A and

Studies in Logic and the Foundations of Mathematics

p. 341–349In this paper a characterization of principal congruences of De Morgan algebras is given and from it we derive that the variety of De Morgan algebras has DPC and CEP. The characterization is then applied to give a new proof of Kalman's characterization of subdirectly irreducibles in this variety and thus to obtain the representation theorem for DeMorgan algebras first proved by Kalman and independently, using topological methods, by Bialynicki-Birula and Rasiowa. From this representation it is deduced that finite De Morgan algebras are not the only ones with Boolean congruence lattices. Finally it is shown that the compact elements in the congruence lattice of a De Morgan algebra form a Boolean sublattice