范畴泛覆盖的存在性
On the Existence of Categorical Universal Coverings
摘要:
本文利用给定空间$X$的开覆盖研究了范畴泛覆盖存在的充要条件。作为某些应用,首先我们给出了Shelah定理(Mycielski猜想:如果$X$是Peano连续统,则$π_1(X,x)$是不可数的或$X$有单连通泛覆盖)的一个推广版本,它指出第一可数Peano空间有范畴泛覆盖或有不可数的基本群.其次,证明了一点并$X_1\vee X_2=\frac{{X_1}\cup {X_2}}{{x_1}\sim {x_2}}$有范畴泛覆盖当且仅当$X_1$和$X_2$都有范畴泛覆盖.
英文摘要:
In this paper, we study necessary and sufficient conditions for the existence of categorical universal coverings using open covers of a given space $X$. As some applications, first we present a generalized version of the Shelah Theorem (Mycielski's conjecture: If $X$ is a Peano continuum, then $π_1(X,x)$ is uncountable or $X$ has a simply connected universal covering) which states that a first countable Peano space has a categorical universal covering or has an uncountable fundamental group. Second, we prove that the one point union $X_1\vee X_2=\frac{{X_1}\cup {X_2}}{{x_1}\sim {x_2}}$ has a categorical universal covering if and only if both $X_1$ and $X_2$ have categorical universal coverings.
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