Small infinite partitions and other features of the Nowhere Centered ideal
The \textit{nowhere dense ideal} $\mathcal{NC}$ is introduced. It is a coanalytic ideal of $\omega\times\omega$ whose defining characteristic is that the sets of the form $X\times Y$, where $X,Y$ are infinite subsets of $\omega$, are dense in the quotient $\mathcal{P}(\omega\times\omega)\slash\mathc...
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Zusammenfassung: | The \textit{nowhere dense ideal} $\mathcal{NC}$ is introduced. It is a
coanalytic ideal of $\omega\times\omega$ whose defining characteristic is that
the sets of the form $X\times Y$, where $X,Y$ are infinite subsets of $\omega$,
are dense in the quotient $\mathcal{P}(\omega\times\omega)\slash\mathcal{NC}$.
This quotient has countable partitions and consistently has partitions of size
$\omega_1$ while $\mathfrak{a}>\omega_1$. This represents a huge contrast with
other definable quotients. Other combinatorial features of this ideal are
presented, as well as some results on a family of similar, higher dimensional
ideals. |
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DOI: | 10.48550/arxiv.2203.00234 |