arXiv subjects

Tamás Dékány

Publications and source records attributed to Tamás Dékány.

3 recordsLinked to original sources

arXiv2018

$E$-solid locally inverse semigroups

We prove that if $S$ is an $E$-solid locally inverse semigroup, and $ρ$ is an inverse semigroup congruence on $S$ such that the idempotent classes of $ρ$ are completely simple semigroups then $S$ is embeddable into a $λ$-semidirect product of a completely simple semigroup by $S/ρ$. Consequently, the $E$-solid locally inverse semigroups turn out to be, up to isomorphism, the regular subsemigroups of $λ$-semidirect products of completely simple semigroups by inverse semigroups.

math.GR↗

arXiv2013

On extensions of completely simple semigroups by groups

An example of an extension of a completely simple semigroup U by a group H is given which cannot be embedded into the wreath product of U by H. On the other hand, every central extension of U by H is shown to be embeddable in the wreath product of U by H, and any extension of U by H is proved to be embeddable in a semidirect product of a completely simple semigroup V by H where the maximal subgroups of V are direct powers of those of U.

math.RA↗

arXiv2012

On the number of slim, semimodular lattices

A lattice L is slim if it is finite and the set of its join-irreducible elements contains no three-element antichain. Slim, semimodular lattices were previously characterized by G. Czédli and E.T. Schmidt as the duals of the lattices consisting of the intersections of the members of two composition series in a group. Our main result determines the number of (isomorphism classes of) these lattices of a given size in a recursive way. The corresponding planar diagrams, up to similarity, are also enumerated. We prove that the number of diagrams of slim, distributive lattices of a given length b is the n-th Catalan number. Besides lattice theory, the paper includes some combinatorial arguments on permutations and their inversions.

math.RA↗