The Cantor-Bernstein theorem was extended to $\sigma$-complete boolean algebras by Sikorski and Tarski. Chang’s MV-algebras are a nontrivial generalization of boolean algebras: they stand to the infinite-valued calculus of Łukasiewicz as boolean algebras stand to the classical two-valued calculus. In this paper we further generalize the Cantor-Bernstein theorem to $\sigma$-complete MV-algebras, and compare it to a related result proved by Jakubík for certain complete MV-algebras.

We discuss the ultrasimplicial property of lattice-ordered abelian groups and their associated MV-algebras. We give a constructive proof of the fact that every lattice-ordered abelian group generated by three elements is ultrasimplicial.

Let $L$ be an MS-algebra with congruence permutable skeleton. We prove that solving a system of congruences $({\theta }_1,...,{\theta }_n;x_1,...,x_n)$ in $L$ can be reduced to solving the restriction of the system to the skeleton of $L$, plus solving the restrictions of the system to the intervals $[x_1,{\overline{\overline{x}}}_1],\cdots ,[x_n,{\overline{\overline{x}}}_n].$

We introduce the concept of a pseudo-Kleene algebra which is a non-distributive modification of a Kleene algebra introduced by J. A. Kalman [Kalman, J. A.: Lattices with involution. Trans. Amer. Math. Soc. 87 (1958), 485–491.]. Basic properties of pseudo-Kleene algebras are studied. For pseudo-Kleene algebras with a fix-point there are determined subdirectly irreducible members.

The paper introduces a definition of symmetric difference in lattices with negation, presents its general properties and studies those that are typical of ortholattices, orthomodular lattices, De Morgan and Boolean algebras.

In 2000, Figallo and Sanza introduced $n\times m$-valued Łukasiewicz-Moisil algebras which are both particular cases of matrix Łukasiewicz algebras and a generalization of $n$-valued Łukasiewicz-Moisil algebras. Here we initiate an investigation into the class tLM${}_{n\times m}$ of tense $n\times m$-valued Łukasiewicz-Moisil algebras (or tense LM${}_{n\times m}$-algebras), namely $n\times m$-valued Łukasiewicz-Moisil algebras endowed with two unary operations called tense operators. These algebras constitute a generalization of tense Łukasiewicz-Moisil algebras...

This short note shows that the scheme of disjunctive reasoning, a or b, not b : a, does not hold neither in proper ortholattices nor in proper de Morgan algebras. In both cases the scheme, once translated into the inequality b' · (a+b) ≤ a, forces the structure to be a boolean algebra.

We prove some properties of quasi-local Ł-algebras. These properties allow us to give a structure theorem for Stonean quasi-local Ł-algebras. With this characterization we are able to exhibit an example which provides a negative answer to the first problem posed in [4].

We introduce Kleene's 3-valued logic in a language containing, besides the Boolean connectives, a constant $n$ for the undefined truth value, so in developing semantics we can switch from the usual treatment based on DM-algebras to the narrower class of DMF-algebras (De Morgan algebras with a single fixed point for negation). A sequent calculus for Kleene's logic is introduced and proved complete with respect to threevalent semantics. The completeness proof is based on a version of the prime ideal...