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arXiv 2302.01006math.LO
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广义Baire空间中闭集的连续象

Continuous images of closed sets in generalized Baire spaces

Philipp Lücke, Philipp Schlicht

摘要:

设$κ$是一个不可数基数,有$κ=κ^{{<}κ}$。给定一个基数$μ$,我们给由从$κ$到$μ$的所有函数组成的集合${}^κμ$赋予一个拓扑,该拓扑的基本开集由基数小于$κ$的部分函数的所有扩张组成.我们证明的结果,使我们能够分离的几个类的${}^κκ$的子集组成的连续图像的闭子集的空间的形式${}^κμ$。这些结果的重要例子如下:(i)存在${}^κκ$的闭子集,其不是${}^κκ$的连续像;(ii)存在${}^κκ$的内射连续像,其不是$κ$ -Borel(即,不包含在包含所有开子集并且在$κ$ -并集下闭合的${}^κκ$上的最小集合代数中);(iii)命题“${}^κκ$的每个连续象是${}^κκ$的闭子集的内射连续象“独立于$\mathrm{ZFC}$的公理;及(iv)$\mathrm{ZFC}$的公理并不证明假设“$2^κ>κ^+$ "隐含陈述“${}^κκ$的每个闭子集是${}^κ(κ^+)$ "或其否定的连续像。

英文摘要:

Let $κ$ be an uncountable cardinal with $κ=κ^{{<}κ}$. Given a cardinal $μ$, we equip the set ${}^κμ$ consisting of all functions from $κ$ to $μ$ with the topology whose basic open sets consist of all extensions of partial functions of cardinality less than $κ$. We prove results that allow us to separate several classes of subsets of ${}^κκ$ that consist of continuous images of closed subsets of spaces of the form ${}^κμ$. Important examples of such results are the following: (i) there is a closed subset of ${}^κκ$ that is not a continuous image of ${}^κκ$; (ii) there is an injective continuous image of ${}^κκ$ that is not $κ$-Borel (i.e. that is not contained in the smallest algebra of sets on ${}^κκ$ that contains all open subsets and is closed under $κ$-unions); (iii) the statement "every continuous image of ${}^κκ$ is an injective continuous image of a closed subset of ${}^κκ$" is independent of the axioms of $\mathrm{ZFC}$; and (iv) the axioms of $\mathrm{ZFC}$ do not prove that the assumption "$2^κ>κ^+$'' implies the statement "every closed subset of ${}^κκ$ is a continuous image of ${}^κ(κ^+)$'' or its negation.

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