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On the cardinality of separable pseudoradial spaces
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
Affiliation  

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 >c. While this question is left open, we establish a number of non-trivial results that we list below.

It is consistent with MA+c=2 that there is a countably tight and compact SP space of cardinality 2c.

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 c.

If κ>1 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 c.

If c2 then there is a 0-dimensional SP space with a countable dense set of isolated points that has cardinality greater than c.



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>C. 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。

它符合 一种+C=2存在可数紧且紧的基数SP空间2C.

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C.

如果 κ>1 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 C.

如果 C2 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 C.

更新日期:2021-07-22
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