Pseudointersection numbers, ideal slaloms, topological spaces, and cardinal inequalities

Archive for Mathematical Logic 62 (1):87-112 (2023)
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Abstract

We investigate several ideal versions of the pseudointersection number p\mathfrak {p}, ideal slalom numbers, and associated topological spaces with the focus on selection principles. However, it turns out that well-known pseudointersection invariant cov(I)\mathtt {cov}^*({\mathcal I}) has a crucial influence on the studied notions. For an invariant pK(J)\mathfrak {p}_\mathrm {K}({\mathcal J}) introduced by Borodulin-Nadzieja and Farkas (Arch. Math. Logic 51:187–202, 2012), and an invariant pK(I,J)\mathfrak {p}_\mathrm {K}({\mathcal I},{\mathcal J}) introduced by Repický (Real Anal. Exchange 46:367–394, 2021), we have min{pK(I),cov(I)}=p,min{pK(I,J),cov(J)}cov(I),\begin{aligned} \min \{\mathfrak {p}_\mathrm {K}({\mathcal I}),\mathtt {cov}^*({\mathcal I})\}=\mathfrak {p},\qquad \min \{\mathfrak {p}_\mathrm {K}({\mathcal I},{\mathcal J}),\mathtt {cov}^*({\mathcal J})\}\le \mathtt {cov}^*({\mathcal I}), \end{aligned} respectively. In addition to the first inequality, for a slalom invariant sle(I,J)\mathfrak {sl_e}({\mathcal I},{\mathcal J}) introduced in Šupina (J. Math. Anal. Appl. 434:477–491, 2016), we show that min{pK(I),sle(I,J),cov(J)}=p.\begin{aligned} \min \{\mathfrak {p}_\mathrm {K}({\mathcal I}),\mathfrak {sl_e}({\mathcal I},{\mathcal J}),\mathtt {cov}^*({\mathcal J})\}=\mathfrak {p}. \end{aligned} Finally, we obtain a consistency that ideal versions of the Fréchet–Urysohn property and the strictly Fréchet–Urysohn property are distinguished.

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References found in this work

Katětov order on Borel ideals.Michael Hrušák - 2017 - Archive for Mathematical Logic 56 (7-8):831-847.
Restricted mad families.Osvaldo Guzmán, Michael Hrušák & Osvaldo Téllez - 2020 - Journal of Symbolic Logic 85 (1):149-165.
Countable ultraproducts without CH.Michael Canjar - 1988 - Annals of Pure and Applied Logic 37 (1):1-79.

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