English

Descriptive properties of I2-embeddings

Logic 2024-11-05 v3

Abstract

We contribute to the study of generalizations of the Perfect Set Property and the Baire Property to subsets of spaces of higher cardinalities, like the power set P(λ)P(\lambda) of a singular cardinal λ\lambda of countable cofinality or products i<ωλi\prod_{i<\omega}\lambda_i for a strictly increasing sequence λi  i<ω\langle\lambda_i ~ \vert ~ i<\omega\rangle of cardinals. We consider the question under which large cardinal hypotheses classes of definable subsets of these spaces possess such regularity properties, focusing on rank-into-rank axioms and classes of sets definable by Σ1\Sigma_1-formulas with parameters from various collections of sets. We prove that ω\omega-many measurable cardinals, while sufficient to prove the Perfect Set Property of all Σ1\Sigma_1-definable sets with parameters in Vλ{Vλ}V_\lambda\cup\{V_\lambda\}, are not enough to prove it if there is a cofinal sequence in λ\lambda in the parameters. For this conclusion, the existence of an I2-embedding is enough, but there are parameters in Vλ+1V_{\lambda+1} for which I2 is still not enough. The situation is similar for the Baire Property: under I2 all sets that are Σ1\Sigma_1-definable using elements of VλV_\lambda and a cofinal sequence as parameters have the Baire property, but I2 is not enough for some parameter in Vλ+1V_{\lambda+1}. Finally, the existence of an I0-embedding implies that all sets that are Σn1\Sigma^1_n-definable with parameters in Vλ+1V_{\lambda+1} have the Baire property.

Keywords

Cite

@article{arxiv.2311.00376,
  title  = {Descriptive properties of I2-embeddings},
  author = {Vincenzo Dimonte and Martina Iannella and Philipp Lücke},
  journal= {arXiv preprint arXiv:2311.00376},
  year   = {2024}
}

Comments

Revised version. 21 pages

R2 v1 2026-06-28T13:08:19.862Z