Dane publikacji
Tom 67
Zeszyt 2
Czasopismo: Bulletin of the Polish Academy of Sciences Mathematics
Strony: 101-124
Data publikacji online: 29.05.2019
Liczba wyświetleń: 0
Liczba pobrań: 0
Wersja elektroniczna
Abstrakt
In set theory without the Axiom of Choice ($\mathsf{AC}$), we investigate the deductive strength and mutual relationships of the following statements:
(1) Every infinite set $X$ has an almost disjoint family $\mathcal{A}$ of infinite subsets of $X$ with $|\mathcal{A}|\not\leq\aleph_{0}$.
(2) Every infinite set $X$ has an almost disjoint family $\mathcal{A}$ of infinite subsets of $X$ with $|\mathcal{A}| \gt \aleph_{0}$.
(3) For every infinite set $X$, every almost disjoint family in $X$ can be extended to a maximal almost disjoint family in $X$.
(4) For every infinite set $X$, no infinite maximal almost disjoint family in $X$ has cardinality $\aleph_{0}$.
(5) For every infinite set $A$, there is a continuum sized almost disjoint family $\mathcal{A}\subseteq A^{\omega}$.
(6) For every free ultrafilter $\mathcal{U}$ on $\omega$ and every infinite set $A$, the ultrapower $A^{\omega}/\mathcal{U}$ has cardinality at least $2^{\aleph_{0}}$.