English

A choice-free cardinal equality

Logic 2021-11-02 v1

Abstract

For a cardinal a\mathfrak{a}, let fin(a)\mathrm{fin}(\mathfrak{a}) be the cardinality of the set of all finite subsets of a set which is of cardinality a\mathfrak{a}. It is proved without the aid of the axiom of choice that for all infinite cardinals a\mathfrak{a} and all natural numbers nn, 2fin(a)n=2[fin(a)]n. 2^{\mathrm{fin}(\mathfrak{a})^n}=2^{[\mathrm{fin}(\mathfrak{a})]^n}. On the other hand, it is proved that the following statement is consistent with ZF\mathsf{ZF}: there exists an infinite cardinal a\mathfrak{a} such that 2fin(a)<2fin(a)2<2fin(a)3<<2fin(fin(a)). 2^{\mathrm{fin}(\mathfrak{a})}<2^{\mathrm{fin}(\mathfrak{a})^2}<2^{\mathrm{fin}(\mathfrak{a})^3}<\dots<2^{\mathrm{fin}(\mathrm{fin}(\mathfrak{a}))}.

Cite

@article{arxiv.1912.12435,
  title  = {A choice-free cardinal equality},
  author = {Guozhen Shen},
  journal= {arXiv preprint arXiv:1912.12435},
  year   = {2021}
}

Comments

12 pages

R2 v1 2026-06-23T12:57:58.258Z