Decomposition of regular subsemigroup lattices

Communicated by Norman R. Reilly     

Varieties of semigroups with non-trivial identities on subsemigroup lattices

The present notice is devoted to the characterization up to the group case of varieties of semigroups whose subsemigroup lattices satisfy non-trivial identities. Received November 2, 1999; accepted in final form April 23, 2000.     

On lattices embeddable into subsemigroup lattices. III: Nilpotent semigroups

We prove that the class of the lattices embeddable into subsemigroup lattices of n-nilpotent semigroups is a finitely based variety for all n < ω. Repnitski? showed that each lattice embeds into the subsemigroup lattice of a commutative nilsemigroup of index 2. In this proof he used a result of Bredikhin and Schein which states that each lattice embeds into the suborder lattices of an appropriate order. We give a direct proof of the Repnitski? result not appealing to the Bredikhin-Schein theorem, so answering a question in a book by Shevrin and Ovsyannikov.     

Lattices embeddable in subsemigroup lattices. II. Cancellative semigroups

Repnitskii proved that any lattice embeds in a subsemigroup lattice of some commutative, cancellative, idempotent free semigroup with unique roots. In that proof, use is made of a result by Bredikhin and Schein stating that any lattice embeds in a suborder lattice of suitable partial order. Here, we present a direct proof of Repnitskii’s result which is independent of Bredikhin-Schein’s, thus giving the answer to the question posed by Shevrin and Ovsyannikov. Supported by INTAS grant No. 03-51-4110; RF Ministry of Education grant No. E02-1.0-32; Council for Grants (under RF President) and State Aid of Fundamental Science Schools, project NSh-2112.2003.1; a grant from the Russian Science Support Foundation; SB RAS Young Researchers Support project No. 11. __________ Translated from Algebra i Logika, Vol. 45, No. 4, pp. 436–446, July–August, 2006.     

On congruence lattices of regular semigroups with Q-inverse transversals

Communicated by F. Pastijn     

On subsemigroup lattices without non-trivial identities

A latticeL is called discriminating if for any free latticeF and for any finite number of elementsu ₁,u ₂, ...,u _nF, there exists a homomorphismf:FL such thatf(u _i )f(u _j ) wheneveru _i u _j (1i, jn). In this paper it is proved that the subsemigroup lattice SubS of a commutative semigroupS does not satisfy a non-trivial identity if and only if SubS is discriminating. In particular, in this case every finite projective lattice can be embedded into SubS. It should be noted that the most important examples of semigroups whose subsemigroup lattices satisfy no non-trivial identity and therefore have the discriminating property are the following: the infinite cyclic semigroup, the free semilattice of countable rank, any commutative nilsemigroup which is not nilpotent and so on.Presented by V. A. Gorbunov.The author thanks Prof. L. N. Shevrin and Dr. M. V. Volkov for a number of useful remarks.     

On subsemigroup lattices of aperiodic groups

This note is inspired by some results and questions from the survey [9] of Shevrin and Ovsyannikov and by Shevrin personally. The author wishes to thank Professor Shevrin for fruitful discussions. In the note some problems related to determinability of aperiodic (=non-torsion) groups by their subsemigroup lattices are settled in the negative. It is worth pointing out that the groups constructed below in the negative. It is worth pointing out that the groups that satisfy the maximal condition for subsemigroups.     

The variety of unary semigroups with associate inverse subsemigroup

In Billhardt et al. (Semigroup Forum 79:101–118, 2009) the authors introduced the notion of an associate inverse subsemigroup of a regular semigroup, extending the concept of an associate subgroup of a regular semigroup, first presented in Blyth et al. (Glasg. Math. J. 36:163–171, 1994). The semigroups of these two classes admit axiomatic characterisations in terms of unary operations and can, therefore, be considered as unary semigroups. In this paper we introduce the notion of unary semigroup with associate inverse subsemigroup [with associate subgroup] and show that the classes of such unary semigroups form varieties.     

On finite lattices which are embeddable in subsemigroup lattices

Communicated by L. N. Shevrin     

On lattices embeddable into subsemigroup lattices. V. Trees

We prove that the class of finite lattices embeddable into the subsemilattice lattices of semilattices which are (n-ary) trees can be axiomatized by identities within the class of finite lattices, whence it forms a pseudovariety.     

Orthodox semigroups with complemented congruence lattices

Communicated by J. M. Howie     

Completely regular semigroups

No abstract. August 22, 2001     

Lattices embeddable in subsemigroup lattices. I. Semilattices

V. B. Repnitskii showed that any lattice embeds in some subsemilattice lattice. In his proof, use was made of a result by D. Bredikhin and B. Schein, stating that any lattice embeds in the suborder lattice of a suitable partial order. We present a direct proof of Repnitskii’s result, which is independent of Bredikhin—Schein’s, giving the answer to a question posed by L. N. Shevrin and A. J. Ovsyannikov. We also show that a finite lattice is lower bounded iff it is isomorphic to the lattice of subsemilattices of a finite semilattice that are closed under a distributive quasiorder. Supported by INTAS grant No. 03-51-4110; RF Ministry of Education grant No. E02-1.0-32; Council for Grants (under RF President) and State Aid of Fundamental Science Schools, project NSh-2112.2003.1; a grant from the Russian Science Support Foundation; SB RAS Young Researchers Support project No. 11. __________ Translated from Algebra i Logika, Vol. 45, No. 2, pp. 215–230, March–April, 2006.