Consequences of arithmetic for set theory

Lorenz Halbeisen; Saharon Shelah

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Consequences of arithmetic for set theory

Lorenz Halbeisen·Saharon Shelah

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Abstract

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 C and D, either C <= D or D <= C. However, in ZF this is no longer so. For a given infinite set A consider Seq(A), the set of all sequences of A without repetition. We compare |Seq(A)|, the cardinality of this set, to |P(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 |- for all A: |Seq(A)| not= |P(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 |fin(B)|<|P(B)|, even though the existence for some infinite set B^* of a function f from fin(B^*) onto P(B^*) is consistent with ZF.

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BibTeX RIS

Lorenz Halbeisen, Saharon Shelah. 1993-08-15. Consequences of arithmetic for set theory. https://arxiv.org/abs/math/9308220

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