Сharacterization of distributive lattices of quasivarieties of unars

V. K. Kartashov ; A. V. Kartashova

Čebyševskij sbornik, Tome 22 (2021) no. 1, pp. 177-187.

Résumé

Let $ L_q (\mathfrak{M}) $ denote the lattice of all subquasivarieties of the quasivariety $\mathfrak{M} $ under inclusion. There is a strong correlation between the properties of the lattice $L_q (\mathfrak {M}) $ and algebraic systems from $\mathfrak{M} $. A. I. Maltsev first drew attention to this fact in a report at the International Congress of Mathematicians in 1966 in Moscow. In this paper, we obtain a characterization of the class of all distributive lattices, each of which is isomorphic to the lattice of some quasivariety of unars. A unar is an algebra with one unary operation. Obviously, any unar can be considered as an automaton with one input signal without output signals, or as an act over a cyclic semigroup. We construct partially ordered sets $P_{\infty} $ and $ P_s (s \in {\mathbf{N}_0})$, where ${\mathbf{N}_0}$ is the set of all non-negative integers. It is proved that a distributive lattice is isomorphic to the lattice $ L_q (\mathfrak{M})$ for some quasivariety of unars $\mathfrak{M} $ if and only if it is isomorphic to some principal ideal of one of the lattices $O (P_s) (s \in {\mathbf{N}_0})$ or $O_c (P_{\infty})$, where $ O (P_s) (s \in {\mathbf{N}_0})$ is the ideal lattice of the poset $ P_s (s \in {\mathbf{N}_0}) $ and $O_c (P_ {\infty})$ is the ideal lattice with a distinguished element $c$ of the poset $P _ {\infty}$. The proof of the main theorem is based on the description of $\mathrm{Q}$-critical unars. A finitely generated algebra is called $\mathrm{Q}$-critical if it does not decompose into a subdirect product of its proper subalgebras. It was previously shown that each quasivariety of unars is determined by its $\mathrm{Q}$-critical unars. This fact is often used to investigate quasivarieties of unars.

Détail

Keywords: quasivariety, unars, distributive lattices.

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