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A note on dual Dedekind finiteness

Logic 2025-09-23 v2

Abstract

A set AA is dually Dedekind finite if every surjection from AA onto AA is injective; otherwise, AA is dually Dedekind infinite. It is proved consistent with ZF\mathsf{ZF} (i.e., the Zermelo--Fraenkel set theory without the axiom of choice) that there exists a family Annω\langle A_n\rangle_{n\in\omega} of sets such that, for all nωn\in\omega, AnnA_n^n is dually Dedekind finite whereas Ann+1A_n^{n+1} is dually Dedekind infinite. This resolves a question that was left open in [J. Truss, Fund. Math. 84, 187--208 (1974)].

Cite

@article{arxiv.2412.07142,
  title  = {A note on dual Dedekind finiteness},
  author = {Ruihuan Mao and Guozhen Shen},
  journal= {arXiv preprint arXiv:2412.07142},
  year   = {2025}
}

Comments

6 pages

R2 v1 2026-06-28T20:28:54.690Z