{"title":"关于三角群可由有限商区分的两个新证明","authors":"M. Conder","doi":"10.53733/193","DOIUrl":null,"url":null,"abstract":"In a 2016 paper by Alan Reid, Martin Bridson and the author, it was shown using the theory of profinite groups that if $\\Gamma$ is a finitely-generated Fuchsian group and $\\Sigma$ is a lattice in a connected Lie group, such that $\\Gamma$ and $\\Sigma$ have exactly the same finite quotients, then $\\Gamma$ is isomorphic to $\\Sigma$. As a consequence, two triangle groups $\\Delta(r,s,t)$ and $\\Delta(u,v,w)$ have the same finite quotients if and only if $(u,v,w)$ is a permutation of $(r,s,t)$. A direct proof of this property of triangle groups was given in the final section of that paper, with the purpose of exhibiting explicit finite quotients that can distinguish one triangle group from another. Unfortunately, part of the latter direct proof was flawed. In this paper two new direct proofs are given, one being a corrected version using the same approach as before (involving direct products of small quotients), and the other being a shorter one that uses the same preliminary observations as in the earlier version but then takes a different direction (involving further use of the `Macbeath trick').","PeriodicalId":30137,"journal":{"name":"New Zealand Journal of Mathematics","volume":"35 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2022-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Two new proofs of the fact that triangle groups are distinguished by their finite quotients\",\"authors\":\"M. Conder\",\"doi\":\"10.53733/193\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"In a 2016 paper by Alan Reid, Martin Bridson and the author, it was shown using the theory of profinite groups that if $\\\\Gamma$ is a finitely-generated Fuchsian group and $\\\\Sigma$ is a lattice in a connected Lie group, such that $\\\\Gamma$ and $\\\\Sigma$ have exactly the same finite quotients, then $\\\\Gamma$ is isomorphic to $\\\\Sigma$. As a consequence, two triangle groups $\\\\Delta(r,s,t)$ and $\\\\Delta(u,v,w)$ have the same finite quotients if and only if $(u,v,w)$ is a permutation of $(r,s,t)$. A direct proof of this property of triangle groups was given in the final section of that paper, with the purpose of exhibiting explicit finite quotients that can distinguish one triangle group from another. Unfortunately, part of the latter direct proof was flawed. In this paper two new direct proofs are given, one being a corrected version using the same approach as before (involving direct products of small quotients), and the other being a shorter one that uses the same preliminary observations as in the earlier version but then takes a different direction (involving further use of the `Macbeath trick').\",\"PeriodicalId\":30137,\"journal\":{\"name\":\"New Zealand Journal of Mathematics\",\"volume\":\"35 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2022-03-03\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"New Zealand Journal of Mathematics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.53733/193\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"Mathematics\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"New Zealand Journal of Mathematics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.53733/193","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"Mathematics","Score":null,"Total":0}
引用次数: 0
摘要
在Alan Reid, Martin Bridson和作者2016年的一篇论文中,利用无限群理论证明,如果$\Gamma$是有限生成的Fuchsian群,$\Sigma$是连通李群中的晶格,使得$\Gamma$和$\Sigma$具有完全相同的有限商,则$\Gamma$与$\Sigma$同构。因此,当且仅当$(u,v,w)$是$(r,s,t)$的置换时,两个三角形群$\Delta(r,s,t)$和$\Delta(u,v,w)$具有相同的有限商。在论文的最后一节给出了三角群的这一性质的直接证明,目的是证明可以区分三角群的显式有限商。不幸的是,后者的部分直接证据是有缺陷的。本文给出了两个新的直接证明,一个是使用与之前相同方法的更正版本(涉及小商的直接乘积),另一个是使用与早期版本相同的初步观察结果的较短版本,但随后采取了不同的方向(涉及进一步使用“麦克白技巧”)。
Two new proofs of the fact that triangle groups are distinguished by their finite quotients
In a 2016 paper by Alan Reid, Martin Bridson and the author, it was shown using the theory of profinite groups that if $\Gamma$ is a finitely-generated Fuchsian group and $\Sigma$ is a lattice in a connected Lie group, such that $\Gamma$ and $\Sigma$ have exactly the same finite quotients, then $\Gamma$ is isomorphic to $\Sigma$. As a consequence, two triangle groups $\Delta(r,s,t)$ and $\Delta(u,v,w)$ have the same finite quotients if and only if $(u,v,w)$ is a permutation of $(r,s,t)$. A direct proof of this property of triangle groups was given in the final section of that paper, with the purpose of exhibiting explicit finite quotients that can distinguish one triangle group from another. Unfortunately, part of the latter direct proof was flawed. In this paper two new direct proofs are given, one being a corrected version using the same approach as before (involving direct products of small quotients), and the other being a shorter one that uses the same preliminary observations as in the earlier version but then takes a different direction (involving further use of the `Macbeath trick').