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Results tagged with cardinal-characteristics
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user 43954
For questions about various cardinal invariants, cardinal characteristics of the continuum and related topics.
5
votes
1
answer
319
views
Bounds for a small cardinal
$\newcommand{\w}{\omega}\newcommand{\F}{\mathcal F}\newcommand{\I}{\mathcal I}\newcommand{\J}{\mathcal J}\newcommand{\M}{\mathcal M}\newcommand{\N}{\mathcal N}\newcommand{\x}{\mathfrak x}\newcommand{\ …
- 5,409
3
votes
1
answer
162
views
Bounds for a covering number of the circle group $\mathbb T$ by some its small subgroups
$\newcommand{\w}{\omega}\newcommand{\A}{\mathcal A}\newcommand{\F}{\mathcal F}\newcommand{\I}{\mathcal I}\newcommand{\J}{\mathcal J}\newcommand{\M}{\mathcal M}\newcommand{\N}{\mathcal N}\newcommand{\x …
- 5,409
7
votes
Accepted
The cardinal characteristic $\mathfrak r_{(X,f)}$ of a dynamical system
Unfortunately, $\mathfrak r_{(2^\omega,f)}\ge\mathfrak r$. Indeed, let $\mathcal R$ be a family of infinite subsets of $\omega$ such that $|\mathcal R|=\mathfrak r_{(2^\omega,f)}$ and for any $x=(x_n) …
- 5,409