It is well known that intra-regular semigroups (ordered semigroups) play an essential role in studying the structure of semigroups (ordered semigroups). In this paper we present a structure theorem referring to the decomposition of ordered semigroups into left strongly simple components, that is, into components, which are both simple and left quasi-regular. We prove, among others, that if an o...

In 1982, L. Iturrioz introduced symmetrical Heyting algebras of order n (or SHnalgebras). In this paper, we define and study tense SHn-algebras namely, SHnalgebras endowed with two tense operators. These algebras constitute a generalization of tense Łukasiewicz-Moisil algebras. Our main interest is the duality theory for tense SHn-algebras. In order to do this, we requiere Esakia’s duality for ...

We show that if a subgroup of the automorphism group Fraïssé limit finite Heyting algebras has countable index, then it lies between pointwise and setwise stabilizer some set.