{"title":"具有补闭子群的无限群","authors":"Gustavo A. Fernández-Alcober, Giulia Sabatino","doi":"10.1016/j.jalgebra.2025.09.013","DOIUrl":null,"url":null,"abstract":"<div><div>A group <em>G</em> is said to be a <em>C</em>-group if every subgroup <em>H</em> has a permutable complement, i.e. if there exists a subgroup <em>K</em> of <em>G</em> such that <span><math><mi>G</mi><mo>=</mo><mi>H</mi><mi>K</mi></math></span> and <span><math><mi>H</mi><mo>∩</mo><mi>K</mi><mo>=</mo><mn>1</mn></math></span>. In this paper, we study the profinite counterpart of this concept. We say that a profinite group <em>G</em> is profinite-<em>C</em> if every closed subgroup admits a closed permutable complement. We first give some equivalent variants of this condition and then we determine the structure of profinite-<em>C</em> groups: they are the semidirect products <span><math><mi>G</mi><mo>=</mo><mi>B</mi><mo>⋉</mo><mi>A</mi></math></span> of two closed subgroups <span><math><mi>A</mi><mo>=</mo><msub><mrow><mi>Cr</mi></mrow><mrow><mi>i</mi><mo>∈</mo><mi>I</mi></mrow></msub><mspace></mspace><mspace></mspace><mo>〈</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>〉</mo></math></span> and <span><math><mi>B</mi><mo>=</mo><msub><mrow><mi>Cr</mi></mrow><mrow><mi>j</mi><mo>∈</mo><mi>J</mi></mrow></msub><mspace></mspace><mspace></mspace><mo>〈</mo><msub><mrow><mi>b</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>〉</mo></math></span> that are cartesian products of cyclic groups of prime order, and with every <span><math><mo>〈</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>〉</mo></math></span> normal in <em>G</em>. Finally, we show that a profinite-<em>C</em> group is a <em>C</em>-group if and only if it is torsion and <span><math><mo>|</mo><mi>G</mi><mo>:</mo><mi>Z</mi><mo>(</mo><mi>G</mi><mo>)</mo><mover><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow><mo>‾</mo></mover><mo>|</mo><mo><</mo><mo>∞</mo></math></span>.</div></div>","PeriodicalId":14888,"journal":{"name":"Journal of Algebra","volume":"687 ","pages":"Pages 763-775"},"PeriodicalIF":0.8000,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Profinite groups with complemented closed subgroups\",\"authors\":\"Gustavo A. Fernández-Alcober, Giulia Sabatino\",\"doi\":\"10.1016/j.jalgebra.2025.09.013\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>A group <em>G</em> is said to be a <em>C</em>-group if every subgroup <em>H</em> has a permutable complement, i.e. if there exists a subgroup <em>K</em> of <em>G</em> such that <span><math><mi>G</mi><mo>=</mo><mi>H</mi><mi>K</mi></math></span> and <span><math><mi>H</mi><mo>∩</mo><mi>K</mi><mo>=</mo><mn>1</mn></math></span>. In this paper, we study the profinite counterpart of this concept. We say that a profinite group <em>G</em> is profinite-<em>C</em> if every closed subgroup admits a closed permutable complement. We first give some equivalent variants of this condition and then we determine the structure of profinite-<em>C</em> groups: they are the semidirect products <span><math><mi>G</mi><mo>=</mo><mi>B</mi><mo>⋉</mo><mi>A</mi></math></span> of two closed subgroups <span><math><mi>A</mi><mo>=</mo><msub><mrow><mi>Cr</mi></mrow><mrow><mi>i</mi><mo>∈</mo><mi>I</mi></mrow></msub><mspace></mspace><mspace></mspace><mo>〈</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>〉</mo></math></span> and <span><math><mi>B</mi><mo>=</mo><msub><mrow><mi>Cr</mi></mrow><mrow><mi>j</mi><mo>∈</mo><mi>J</mi></mrow></msub><mspace></mspace><mspace></mspace><mo>〈</mo><msub><mrow><mi>b</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>〉</mo></math></span> that are cartesian products of cyclic groups of prime order, and with every <span><math><mo>〈</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>〉</mo></math></span> normal in <em>G</em>. Finally, we show that a profinite-<em>C</em> group is a <em>C</em>-group if and only if it is torsion and <span><math><mo>|</mo><mi>G</mi><mo>:</mo><mi>Z</mi><mo>(</mo><mi>G</mi><mo>)</mo><mover><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow><mo>‾</mo></mover><mo>|</mo><mo><</mo><mo>∞</mo></math></span>.</div></div>\",\"PeriodicalId\":14888,\"journal\":{\"name\":\"Journal of Algebra\",\"volume\":\"687 \",\"pages\":\"Pages 763-775\"},\"PeriodicalIF\":0.8000,\"publicationDate\":\"2025-10-06\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Algebra\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0021869325005447\",\"RegionNum\":2,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Algebra","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0021869325005447","RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
摘要
如果子群H有一个置换补,即存在G的子群K使G=HK且H∩K=1,则群G是c群。在本文中,我们研究了这个概念的无限对应物。如果每个闭子群都有一个闭置换补,我们就说一个无限群G是有限群c。我们首先给出了这个条件的一些等价变体,然后我们确定了prolimited - c群的结构:它们是两个闭子群A=Cri∈I < ai >和B=Crj∈J < bj >的半直积G=B × A,它们是素阶循环群的笛卡尔积,并且在G中每一个< ai >正规,最后我们证明了prolimited - c群是c群当且仅当它是扭转和|G:Z(G)G ' ' |<∞。
Profinite groups with complemented closed subgroups
A group G is said to be a C-group if every subgroup H has a permutable complement, i.e. if there exists a subgroup K of G such that and . In this paper, we study the profinite counterpart of this concept. We say that a profinite group G is profinite-C if every closed subgroup admits a closed permutable complement. We first give some equivalent variants of this condition and then we determine the structure of profinite-C groups: they are the semidirect products of two closed subgroups and that are cartesian products of cyclic groups of prime order, and with every normal in G. Finally, we show that a profinite-C group is a C-group if and only if it is torsion and .
期刊介绍:
The Journal of Algebra is a leading international journal and publishes papers that demonstrate high quality research results in algebra and related computational aspects. Only the very best and most interesting papers are to be considered for publication in the journal. With this in mind, it is important that the contribution offer a substantial result that will have a lasting effect upon the field. The journal also seeks work that presents innovative techniques that offer promising results for future research.