Consequences of Arithmetic for Set Theory
Halbeisen, Lorenz ; Shelah, Saharon
J. Symbolic Logic, Tome 59 (1994) no. 1, p. 30-40 / Harvested from Project Euclid
In this paper, we consider certain cardinals in ZF (set theory without AC, the axiom of choice). In ZFC (set theory with AC), given any cardinals $\mathscr{C}$ and $\mathscr{D}$, either $\mathscr{C} \leq \mathscr{D}$ or $\mathscr{D} \leq \mathscr{C}$. However, in ZF this is no longer so. For a given infinite set $A$ consider $\operatorname{seq}^{1 - 1}(A)$, the set of all sequences of $A$ without repetition. We compare $|\operatorname{seq}^{1 - 1}(A)|$, the cardinality of this set, to $|\mathscr{P}(\mathscr{A})|$, the cardinality of the power set of $A$. What is provable about these two cardinals in ZF? The main result of this paper is that $ZF \vdash \forall A(|\operatorname{seq}^{1 - 1}(A)| \neq|\mathscr{P}(\mathscr{A})|)$, and we show that this is the best possible result. Furthermore, it is provable in ZF that if $B$ is an infinite set, then $|\operatorname{fin}(B)| < |\mathscr{P}(B)|$ even though the existence for some infinite set $B^\ast$ of a function $f$ from $\operatorname{fin}(B^\ast)$ onto $\mathscr{P}(B^\ast)$ is consistent with ZF.
Publié le : 1994-03-14
Classification: 
@article{1183744431,
     author = {Halbeisen, Lorenz and Shelah, Saharon},
     title = {Consequences of Arithmetic for Set Theory},
     journal = {J. Symbolic Logic},
     volume = {59},
     number = {1},
     year = {1994},
     pages = { 30-40},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1183744431}
}
Halbeisen, Lorenz; Shelah, Saharon. Consequences of Arithmetic for Set Theory. J. Symbolic Logic, Tome 59 (1994) no. 1, pp.  30-40. http://gdmltest.u-ga.fr/item/1183744431/