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arXiv 1206.5949math.GN
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关于自由仿拓扑群的拓扑。II

On the topology of free paratopological groups. II

Ali Sayed Elfard, Peter Nickolas

摘要:

设$\FP(X)$是拓扑空间$X$上的自由仿拓扑群.对于$n\in \N$,用$\FP_n(X)$表示$\FP(X)$的子集,该子集由长度最多为$n$的所有字组成,用$i_n$表示从$(X\oplus X^{-1}\oplus \{e\})^n$到$\FP_n(X)$的自然映射。本文在$\FP_2(X)$中找到了一个以单位元$e$为邻域基的邻域基,并给出了$i_2\colon (X\oplus X^{-1}_d\oplus \{e\})^2\to \FP_2(X)$是商映射的若干特征,其中$X$是$T_1$空间,$X^{-1}_d$表示具有离散拓扑的集合$X^{-1}$.在$X$是传递的$T_1$空间的情况下,给出了进一步的特征。还研究了几个特定的空间和空间类。例如,$i_2$是$\R$的每个可数子空间的商,$i_2$不是$\R$的任何不可数紧子空间的商,并且在ZFC中无法判定是否存在$\R$的不可数子空间,其中$i_2$是商。

英文摘要:

Let $\FP(X)$ be the free paratopological group on a topological space $X$. For $n\in \N$, denote by $\FP_n(X)$ the subset of $\FP(X)$ consisting of all words of reduced length at most $n$, and by $i_n$ the natural mapping from $(X\oplus X^{-1}\oplus \{e\})^n$ to $\FP_n(X)$. In this paper a neighbourhood base at the identity $e$ in $\FP_2(X)$ is found. A number of characterisations are then given of the circumstances under which $i_2\colon (X\oplus X^{-1}_d\oplus \{e\})^2\to \FP_2(X)$ is a quotient map, where $X$ is a $T_1$ space and $X^{-1}_d$ denotes the set $X^{-1}$ equipped with the discrete topology. Further characterisations are given in the case where $X$ is a transitive $T_1$ space. Several specific spaces and classes of spaces are also examined. For example, $i_2$ is a quotient for every countable subspace of $\R$, $i_2$ is not a quotient for any uncountable compact subspace of $\R$, and it is undecidable in ZFC whether an uncountable subspace of $\R$ exists for which $i_2$ is a quotient.

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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