Topology and its Applications ( IF 0.6 ) Pub Date : 2021-07-21 , DOI: 10.1016/j.topol.2021.107791 Alan Dow 1 , István Juhász 2
The aim of this paper is to consider questions concerning the possible maximum cardinality of various separable pseudoradial (in short: SP) spaces. The most intriguing question here is if there is in ZFC a regular (or just Hausdorff) SP space of cardinality . While this question is left open, we establish a number of non-trivial results that we list below.
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It is consistent with that there is a countably tight and compact SP space of cardinality .
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If κ is a measurable cardinal then in the forcing extension obtained by adding κ many Cohen reals, every countably tight regular SP space has cardinality at most .
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If Cohen reals are added to a model of GCH then in the extension every pseudocompact SP space with a countable dense set of isolated points has cardinality at most .
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If then there is a 0-dimensional SP space with a countable dense set of isolated points that has cardinality greater than .
中文翻译:
关于可分离伪径向空间的基数
本文的目的是考虑有关各种可分离伪径向(简称:SP)空间的可能最大基数的问题。这里最有趣的问题是在 ZFC 中是否有一个常规的(或只是 Hausdorff)SP 基数空间. 虽然这个问题是悬而未决的,但我们建立了以下列出的一些重要结果。
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它符合 存在可数紧且紧的基数SP空间.
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如果κ是可测基数,那么在通过将κ添加许多 Cohen 实数获得的强制扩展中,每个可数紧的正则 SP 空间至多具有基数.
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如果 将 Cohen 实数添加到 GCH 模型中,然后在扩展中,每个具有可数稠密孤立点集的伪紧 SP 空间至多具有基数 .
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如果 那么有一个 0 维 SP 空间,其中有一个可数的密集孤立点集,其基数大于 .