Mutually permutable subgroups and Fitting classes

Let G = AB be the mutually permutable product of the subgroups A and B. It is shown that if A and B are contained in a Fitting class , then the commutator subgroup G′ of G is also contained in . Received: 14 August 2006 Revised: 17 September 2006     

Two-generator subgroups of soluble groups and their Fitting subgroups

For soluble groups, the Fitting length is bounded by a function of the maximum order of the Fitting subgroups of 2-generator subgroups.     

The influence of $\pi$-quasinormality of some subgroups of a finite group

A subgroup H of G is said to be $\pi$-quasinormal in G if it permute with every Sylow subgroup of G. In this paper, we extend the study on the structure of a finite group under the assumption that some subgroups of G are $\pi$-quasinormal in G. The main result we proved in this paper is the following:Theorem 3.4. Let ${\cal F}$ be a saturated formation containing the supersolvable groups. Suppose that G is a group with a normal subgroup H such that $G/H \in {\cal F}$, and all maximal subgroups of any Sylow subgroup of $F^{*}(H)$ are $\pi$-quasinormal in G, then $G \in {\cal F}$. Received: 10 May 2002     

Mutually permutable products and conjugacy classes

The question of how certain arithmetical conditions on the lengths of the conjugacy classes of a finite group G influence the group structure has been studied by several authors with many results available. The purpose of this paper is to analyse the restrictions imposed by the lengths of the conjugacy classes of some elements of the factors of a finite group G = G ₁ G ₂ · · · G _r , which is the product of the pairwise mutually permutable subgroups G ₁, G ₂, . . . , G _r , on its structure. Some earlier results appear as corollaries of our main theorems.     

On a conjecture about orders of products of elements in the symmetric group

For any $a,b,c,n\in \mathbb{N}$ with $1<a,b,c\le n?2$, then there exist $\alpha ,\beta \in S_n$ such that $o(\alpha )=a$, $o(\beta )=b$ and $o(\alpha \beta )=c$. This is a conjecture of Stefan Kohl and which is closely related to problem on covers of the complex projective line. In this note we prove the conjecture is true.     

On second maximal subgroups of Sylow subgroups of finite groups

Finite groups in which the second maximal subgroups of the Sylow p-subgroups, p a fixed prime, cover or avoid the chief factors of some of its chief series are completely classified.     

The influence of minimal subgroups of focal subgroups on the structure of finite groups

A subgroup H of a finite group G is said to be complemented in G if there exists a subgroup K of G such that G=HK and H∩K=1. In this paper, it is proved that a finite group G is p-nilpotent provided p is the smallest prime number dividing the order of G and every minimal subgroup of the p-focal subgroup of G is complemented in N_G(P), where P is a Sylow p-subgroup of G. As some applications, some interesting results related with complemented minimal subgroups of focal subgroups are obtained.     

Rings and semigroups with permutable zero products

We consider rings R, not necessarily with 1, for which there is a nontrivial permutation σ on n letters such that x₁?x_n=0 implies x_σ(1)?x_σ(n)=0 for all x₁,…,x_n∈R. We prove that this condition alone implies very strong permutability conditions for zero products with sufficiently many factors. To this end we study the infinite sequences of permutation groups P_n(R) consisting of those permutations σ on n letters for which the condition above is satisfied in R. We give the full characterization of such sequences both for rings and for semigroups with 0. This enables us to generalize some recent results by Cohn on reversible rings and by Lambek, Anderson and Camillo on rings and semigroups whose zero products commute. In particular, we prove that rings with permutable zero products satisfy the Köthe conjecture.     

Construction of classes of subgroups of small index in p-groups

A new algorithm to calculate the conjugacy classes of subgroups of index p and p ² of a p-group is presented. It uses a surprising relation between the commutator subgroup of a p-group and linear algebra. The algorithm is by magnitudes faster and uses much less memory than the usual “Neubüser-Felsch” algorithm. However, it is restricted to this special case.     

On c-normality of certain subgroups of prime power order of finite groups

In this paper, we study the structure of the finite group G given that certain subgroups of prime power order are well-situated, which means that they are normally complemented modulo their normal core.Received: 14 October 2004; revised: 12 January 2005     

On the normal indices of proper subgroups of finite groups

We extended the normal index from maximal subgroups to proper subgroups. We give a quantitative version of all results obtained by using c-normal subgroups and obtain some new characterizations of solvable, supersolvable and nilpotent groups by the normal indices of proper subgroups.     

A characterization of the hypercyclically embedded subgroups of finite groups

A normal subgroup H of a finite group G is said to be hypercyclically embedded in G if every chief factor of G below H is cyclic. The major aim of the present paper is to characterize the normal hypercyclically embedded subgroups E of a group G by means of the embedding of the maximal and minimal subgroups of the Sylow subgroups of the generalized Fitting subgroup of E.     

Influence of permutizers of subgroups on the structure of finite groups

A group G is said to satisfy the maximal permutizer condition if the permutizer of any maximal subgroup M of G in G, P_G(M), is G. In this paper, we characterize the supersolubility of finite groups by using the maximal permutizer condition. We also get some results for when both G/N and N are supersoluble, which implies that G is supersoluble. Our results unify or generalize some known results.     

Products of two groups containing cyclic subgroups of index at most 2

It is proved that every group of the form G = AB with subgroups A and B each of which has a cyclic subgroup of index at most 2 is metacyclicby-finite. Received: 13 July 2007     

Finite traces and representations of the group of infinite matrices over a finite field

The article is devoted to the representation theory of locally compact infinite-dimensional group GLB$\mathbb{GLB}$ of almost upper-triangular infinite matrices over the finite field with q   elements. This group was defined by S.K., A.V., and Andrei Zelevinsky in 1982 as an adequate n=∞$n=\infty$ analogue of general linear groups GL(n,q)$\mathbb{GL}(n,q)$. It serves as an alternative to GL(∞,q)$\mathbb{GL}(\infty ,q)$, whose representation theory is poor.     

On connected transversals to abelian subgroups and loop theoretical consequences

In this paper one of our questions is the following: Which finite abelian groups are (are not) isomorphic to inner mapping groups of loops? It is well known that if the inner mapping group of a finite loop Q is abelian, then Q is centrally nilpotent. The other question is: Which properties of abelian inner mapping groups imply the central nilpotency of class at most two of the loop? After reminding the reader of the known results we show new ones. To solve these problems we transform them into group theoretical problems, then using connected transversals we get some answer. Received: 1 December 2004; revised: 8 November 2005     

Notes on the length of conjugacy classes of finite groups

The purpose of this paper is to investigate influences of lengths of conjugacy classes of finite groups on the structure of finite groups. We get a necessary and sufficient condition for a finite group G to be equal to O_p(G)×O_p^′(G). We also generalize some results (Comm. Algebra 27 (9) (1999) 4347).     

Problems related to the Lockett Conjecture on Fitting classes of finite groups

The existence of a solvable non-normal Fitting class F which is not a Lockett class but for which the Lockett Conjecture still holds are studied. We also prove that there exists an ω-local Fitting class F which does not satisfy the Lockett conjecture but the Lockett conjecture still holds under a given condition. As a consequence of our result, a generalized version of the Lausch's problem in the well-known Kourovka Notebook is answered.