The theory of quasivarieties constitutes an independent direction in algebra and
mathematical logic and specializes in a fragment of first-order logic-the so-called universal …

A number of authors, particularly those studying" intermediate" intuit\onistjc logic, have
asked whether a given logic is structurally complete. See [14] and [12] for example. Roughly …

A deductive system is structurally complete if all of its admissible inference rules are
derivable. For several important systems, like the modal logic S5, failure of structural …

It is shown that substructural logics of k-potent BL-algebras and k-potent hoops have unitary
unification (in fact, transparent unifiers) while Basic Fuzzy Logic, BL (the logic of BL …

This paper considers the lattice of subquasivarieties of a regular variety. In particular we
show that if V is a strongly irregular variety that is minimal as a quasivariety, then the …

The paper describes the isomorphic lattices of quasivarieties of commutative quasigroup
modes and of cancellative commutative binary modes. Each quasivariety is characterised by …

Let N={1,…, n}. Which subsets Q of N× N have the property that whenever a ij for (i, j)∈ Q
form a “partial inverse M-matrix”(ie, a ij⩾ 0 and if L× L⊆ Q, then the inverse of {a ij: i, j∈ L} is …

In an earlier paper the authors described the isomorphic lattices of quasivarieties of
commutative quasigroup modes and of cancellative commutative binary modes. This paper …

The aim of the present paper is to describe the structure of hypersimple rings, ie rings over
which injective hulls of simple modules are cyclic. In particular, hypersimple duo rings are …

A deductive system is structurally complete if its admissible inference rules are derivable.
For several important systems, like modal logic S5, failure of structural completeness is …