English

Four Cardinals and Their Relations in ZF

Logic 2023-02-07 v2

Abstract

For a set MM, fin(M)\operatorname{fin}(M) denotes the set of all finite subsets of MM, M2M^2 denotes the Cartesian product M×MM\times M, [M]2[M]^2 denotes the set of all 22-element subsets of MM, and seq11(M)\operatorname{seq}^{1-1}(M) denotes the set of all finite sequences without repetition which can be formed with elements of MM. Furthermore, for a set SS, let S|S| denote the cardinality of SS. Under the assumption that the four cardinalities [M]2|[M]^2|, M2|M^2|, fin(M)|\operatorname{fin}(M)|, seq11(M)|\operatorname{seq}^{1-1}(M)| are pairwise distinct and pairwise comparable in ZF, there are six possible linear orderings between these four cardinalities. We show that at least five of the six possible linear orderings are consistent with ZF.

Keywords

Cite

@article{arxiv.2109.11315,
  title  = {Four Cardinals and Their Relations in ZF},
  author = {Lorenz Halbeisen and Riccardo Plati and Salome Schumacher and Saharon Shelah},
  journal= {arXiv preprint arXiv:2109.11315},
  year   = {2023}
}

Comments

19 pages, 1 figure