Generalized Majority-Minority Operations are Tractable

Generalized majority-minority (GMM) operations are introduced as a common generalization of near unanimity operations and Mal'tsev operations on finite sets. We show that every instance of the constraint satisfaction problem (CSP), where all constraint relations are invariant under a (fixed) GMM operation, is solvable in polynomial time. This constitutes one of the largest tractable cases of the CSP

Solving promise equations over monoids and groups

We give a complete complexity classification for the problem of finding a solution to a given system of equations over a fixed finite monoid, given that a solution over a more restricted monoid exists. As a corollary, we obtain a complexity classification for the same problem over groups

The Subpower Membership Problem for Finite Algebras with Cube Terms

The subalgebra membership problem is the problem of deciding if a given element belongs to an algebra given by a set of generators. This is one of the best established computational problems in algebra. We consider a variant of this problem, which is motivated by recent progress in the Constraint Satisfaction Problem, and is often referred to as the Subpower Membership Problem (SMP). In the SMP we are given a set of tuples in a direct product of algebras from a fixed finite set $\mathcal{K}$ of finite algebras, and are asked whether or not a given tuple belongs to the subalgebra of the direct product generated by a given set. Our main result is that the subpower membership problem SMP($\mathcal{K}$) is in P if $\mathcal{K}$ is a finite set of finite algebras with a cube term, provided $\mathcal{K}$ is contained in a residually small variety. We also prove that for any finite set of finite algebras $\mathcal{K}$ in a variety with a cube term, each one of the problems SMP($\mathcal{K}$), SMP($\mathbb{HS} \mathcal{K}$), and finding compact representations for subpowers in $\mathcal{K}$, is polynomial time reducible to any of the others, and the first two lie in NP

Csoportok és reprezentációik = Groups and their representations

Változatos kérdéseket vizsgáltunk a csoportelméletben, a csoportok reprezentációelméletében és más kapcsolódó absztrakt algebrai területeken. 39 tudományos dolgozatot publikáltunk, ezek nagy részét vezető nemzetközi folyóiratokban (pl. Bulletin of the London Mathematical Society, Duke Mathematical Journal, European Journal of Combinatorics, Journal of Algebra, Journal of Group Theory, Proceedings of the American Mathematical Society). Legfontosabb eredményeink a következők: Meghatároztuk a pozitiv karakterisztikájú globális testek feletti aritmetikai csoportok kongruenciarészcsoport-növekedését. Új példákat találtunk olyan csoportokra, amelyeknek izomorf a pro-véges lezárásuk. Teljes leirását adtuk azoknak a moduláris csoportalgebráknak, melyek Lie nilpotencia-indexe maximális. Csoportelméleti módszereket alkalmazva a loopok elméletében olyan (128 elemű) loopot konstruáltunk, amelynél a belső permutációk csoportja kommutativ és a loop nilpotnecia osztálya 3, ezzel Bruck egy 60 éves kérdésére adtunk választ. Az univerzális algebrában a véges moduláris hálók egy széles osztályára konstruáltunk véges kongruencia-reprezentációkat, mégpedig operátorcsoportok felhasználásával. A bonyolultságelméletben több algebrai problémát tanulmányoztunk. Például megmutattuk, hogy nem feloldható csoportokban az azonosságok ellenőrzése NP-teljes probléma. | We studied various questions in group theory, in representation theory of groups, and in related areas of abstract algebra. We published 39 research papers, many of them in leading international journals (for example, Bulletin of the London Mathematical Society, Duke Mathematical Journal, European Journal of Combinatorics, Journal of Algebra, Journal of Group Theory, Proceedings of the American Mathematical Society). The most important results are the following: We determined the congruence subgroup growth of arithmetic groups over global fields of positive characteristic. We found new examples of groups with isomorphic pro-finite closure. We gave a complete description of modular group algebras with maximal Lie nilpotency index. Applying group theoretic methods in loop theory, we constructed an example of a loop (of order 128) with an Abelian inner permutation group and of nilpotency class 3, thereby answering a 60-year old question of Bruck. In universal algebra we constructed finite congruence lattice representations for a large class of finite modular lattices, namely by using operator groups. In complexity theory we studied several algebraic problems. For example, we showed that for nonsolvable groups the checking of identities is an NP-complete problem