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arXiv 0811.2580math.AT
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分层空间的基本范畴

The fundamental category of a stratified space

Jonathan Woolf

摘要:

局部0和1-连通空间的基本广群分类覆盖空间,或等价的局部系统。当空间是拓扑分层的时候,Treumann基于MacPherson的未发表的思想,构造了一个“退出范畴”(在本文的术语中,“基本范畴”),它对可构造层进行分类,等价于分层的etale覆盖。本文将这种构造推广到同伦分层集,此外还表明基本范畴对可构造的余层进行双重分类,等价分层分支覆盖。更通用的设置有几个优点。它使我们能够消除一个技术'驯服'的条件出现在Treumann的工作,以表明,基本广群可以恢复所有的态射,也许最重要的是,以减少计算的两个阶层的情况下。这提供了一种方法来计算的基本范畴的层和同伦链接的同伦群。我们应用这些技巧来计算R^2的对称积的基本范畴,这些对称积是由碰撞分层的。两个附录分别解释了过滤空间和预序空间之间的密切关系,以及上层和分支覆盖(技术上局部连通的完全扩展)之间的密切关系。

英文摘要:

The fundamental groupoid of a locally 0 and 1-connected space classifies covering spaces, or equivalently local systems. When the space is topologically stratified Treumann, based on unpublished ideas of MacPherson, constructed an `exit category' (in the terminology of this paper, the `fundamental category') which classifies constructible sheaves, equivalently stratified etale covers. This paper generalises this construction to homotopically stratified sets, in addition showing that the fundamental category dually classifies constructible cosheaves, equivalently stratified branched covers. The more general setting has several advantages. It allows us to remove a technical `tameness' condition which appears in Treumann's work; to show that the fundamental groupoid can be recovered by inverting all morphisms and, perhaps most importantly, to reduce computations to the two stratum case. This provides an approach to computing the fundamental category in terms of homotopy groups of strata and homotopy links. We apply these techniques to compute the fundamental category of symmetric products of R^2, stratified by collisions. Two appendices explain the close relations respectively between filtered and pre-ordered spaces and between cosheaves and branched covers (technically locally-connected uniquely-complete spreads).

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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