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Uncountable groups and the geometry of inverse limits of coverings
Topology and its Applications ( IF 0.6 ) Pub Date : 2021-07-12 , DOI: 10.1016/j.topol.2021.107769
Gregory R. Conner 1 , Wolfgang Herfort 2 , Curtis Kent 1 , Petar Pavešić 3
Affiliation  

In this paper we develop a new approach to the study of uncountable fundamental groups by using Hurewicz fibrations with the unique path-lifting property (lifting spaces for short) as a replacement for covering spaces. In particular, we consider the inverse limit of a sequence of covering spaces of X. It is known that the path-connectivity of the inverse limit can be expressed by means of the derived inverse limit functor lim1, which is, however, notoriously difficult to compute when the fundamental group, π1(X), is uncountable. To circumvent this difficulty, we express the set of path-components of the inverse limit X˜ of a sequence of covering spaces in terms of the functors lim and lim1 applied to sequences of countable groups arising from polyhedral approximations of X.

A consequence of our computation is that path-connectedness of a lifting space, X˜, implies that π1(X˜) supplements π1(X) in πˇ1(X) where πˇ1(X) is the inverse limit of fundamental groups of polyhedral approximations of X. As an application we show that GKerZ(Fˆ)=FˆGKerB(1,n)(Fˆ), where Fˆ is the canonical inverse limit of finite rank free groups, G is the fundamental group of the Hawaiian Earring, B(1,n) is the Baumslag-Solitar group, and KerA(Fˆ) is the intersection of kernels of homomorphisms from Fˆ to A.



中文翻译:

不可数群和覆盖物逆极限的几何

在本文中,我们通过使用具有独特路径提升特性(简称提升空间)的Hurewicz 纤维作为覆盖空间的替代,开发了一种研究不可数基本群的新方法。特别地,我们考虑X的覆盖空间序列的逆极限。已知逆极限的路径连通性可以通过导出的逆极限函子来表示1,然而,这是出了名的难以计算,当基本群, π1(X),不可数。为了规避这个困难,我们表达了逆极限的路径分量集X 用函子表示的覆盖空间序列 1应用于由X 的多面体逼近产生的可数群序列。

我们计算的结果是提升空间的路径连通性, X, 暗示 π1(X) 补充剂 π1(X)πˇ1(X) 在哪里 πˇ1(X)X的多面体近似的基本群的逆极限。作为一个应用程序,我们表明G克尔Z(F^)=F^G克尔(1,n)(F^), 在哪里 F^ 是有限秩自由群的规范逆极限, G 是夏威夷耳环的基本组, (1,n) 是 Baumslag-Solitar 群,并且 克尔一种(F^) 是来自同态的核的交集 F^A

更新日期:2021-07-28
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