RUS  ENG
Full version
JOURNALS // Izvestiya Rossiiskoi Akademii Nauk. Seriya Matematicheskaya // Archive

Izv. RAN. Ser. Mat., 2022 Volume 86, Issue 6, Pages 79–100 (Mi im9277)

When is the search of relatively maximal subgroups reduced to quotient groups?

Wen Bin Guoab, D. O. Revincde

a School of Science, Hainan University, Haikou, Hainan, P. R. China
b Department of Mathematics, University of Science and Technology of China, Hefei, P. R. China
c Sobolev Institute of Mathematics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk
d N.N. Krasovskii Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg
e Novosibirsk State University

Abstract: Let $\mathfrak{X}$ be a class finite groups closed under taking subgroups, homomorphic images, and extensions, and let $\mathrm{k}_{\mathfrak{X}}(G)$ be the number of conjugacy classes $\mathfrak{X}$-maximal subgroups of a finite group $G$. The natural problem calling for a description, up to conjugacy, of the $\mathfrak{X}$-maximal subgroups of a given finite group is not inductive. In particular, generally speaking, the image of an $\mathfrak{X}$-maximal subgroup is not $\mathfrak{X}$-maximal in the image of a homomorphism. Nevertheless, there exist group homomorphisms that preserve the number of conjugacy classes of maximal $\mathfrak{X}$-subgroups (for example, the homomorphisms whose kernels are $\mathfrak{X}$-groups). Under such homomorphisms, the image of an $\mathfrak{X}$-maximal subgroup is always $\mathfrak{X}$-maximal, and, moreover, there is a natural bijection between the conjugacy classes of $\mathfrak{X}$-maximal subgroups of the image and preimage. In the present paper, all such homomorphisms are completely described. More precisely, it is shown that, for a homomorphism $\phi$ from a group $G$, the equality $\mathrm{k}_{\mathfrak{X}}(G)=\mathrm{k}_{\mathfrak{X}}(\operatorname{im} \phi)$ holds if and only if $\mathrm{k}_{\mathfrak{X}}(\ker \phi)=1$, which in turn is equivalent to the fact that the composition factors of the kernel of $\phi$ lie in an explicitly given list.

Keywords: finite group, complete class, $\mathfrak{X}$-maximal subgroup, Hall subgroup, reduction $\mathfrak{X}$-theorem.

UDC: 512.542

MSC: 20F28, 20D06, 20E22

Received: 29.10.2021
Revised: 30.01.2022

DOI: 10.4213/im9277


 English version:
Izvestiya: Mathematics, 2022, 86:6, 1102–1122

Bibliographic databases:


© Steklov Math. Inst. of RAS, 2024