It is proved that epimorphisms are surjective in a range of varieties of residuated structures, including all varieties of Heyting or Brouwerian algebras of finite depth, and all varieties consisting of Gödel algebras, relative Stone algebras, Sugihara monoids or positive Sugihara monoids. This establishes the infinite deductive Beth definability property for a corresponding range of substructu...

Algebras axiomatized entirely by rank 1 axioms are algebras for a functor and thus the free algebras can be obtained by a direct limit process. Dually, the final coalgebras can be obtained by an inverse limit process. In order to explore the limits of this method we look at Heyting algebras which have mixed rank 0-1 axiomatizations. We will see that Heyting algebras are special in that they are...

A Heyting algebra is supplemented if each element a has dual pseudo-complement $$a^+$$ , and centrally supplement it central. We show that extension in the same variety of algebras as original. use this tool to investigate new type completion arising context algebraic proof theory, so-called hyper-MacNeille completion. MacNeille its extension. This provides an description algebra, allows develo...

We refine the arithmetical hierarchy of various classical principles by finely investigating derivability relations between these over Heyting arithmetic. mainly investigate some restricted versions law excluded middle, De Morgan's law, double negation elimination, collection principle and constant domain axiom.

Based on the paper [4] we show that true second-order arithmetic is interpretable over real-algebraic structure of models intuitionistic analysis built upon a certain class complete Heyting algebras.

The Alexander dual of an arbitrary meet-semilattice is described explicitly. Meet-distributive meet-semilattices whose Alexander dual is level are characterized.

1. Introduction. A meet semilattice is said to be weakly relatively pseudocomplemented, or just wr-pseudocomplemented, if, for every element x and every y ≤ x, all the maxima