The aim of the paper is to show that topoi are useful in the categorial analysis of the constructive logic with strong negation. In any topos ϵ we can distinguish an object Λ and its truth-arrows such that sets ϵ have a Nelson algebra structure. The object Λ is defined by the categorial counterpart of the algebraic FIDEL-VAKARELOV construction. Then it is possible to define the universal quantifier morphism which permits us to make the first order predicate calculus. The completeness (...) theorem is proved using the Kripke-type semantic defined by THOMASON. (shrink)

The notion of a pseudo-interior algebra was introduced by Blok and Pigozzi in [3]. We continue here our studies begun in [6]. As a consequence of the representation theorem for pseudo-interior algebras given in [6] we prove that the variety of all pseudo-interior algebras has the amalgamation property. Using algebraic methods of Bergman [1] we find infinitely many varieties of pseudo-interior algebras with this property.

The notion of a pseudo-interior algebra was introduced by Blok and Pigozzi in [3]. We continue here our studies begun in [6]. As a consequence of the representation theorem for pseudo-interior algebras given in [6] we prove that the variety of all pseudo-interior algebras has the amalgamation property. Using algebraic methods of Bergman [1] we find infinitely many varieties of pseudo-interior algebras with this property.

The notion of a pseudo-interior algebra was introduced by Blok and Pigozzi in [BPIV]. We continue here our studies begun in [BK]. As a consequence of the representation theorem for pseudo-interior algebras given in [BK] we prove that the variety of all pseudo-interior algebras is generated by its finite members. This result together with Jónsson's Theorem for congruence distributive varieties provides a useful technique in the study of the lattice of varieties of pseudo-interior algebras.