English

On a conjecture of Debs and Saint Raymond

Logic 2025-01-06 v4

Abstract

Borel separation rank of an analytic ideal I\mathcal{I} on ω\omega is the minimal ordinal α<ω1\alpha<\omega_{1} such that there is SΣ1+α0\mathcal{S}\in\bf{\Sigma^0_{1+\alpha}} with IS\mathcal{I}\subseteq \mathcal{S} and IS=\mathcal{I}^\star\cap \mathcal{S}=\emptyset, where I\mathcal{I}^\star is the filter dual to the ideal I\mathcal{I}. Answering in negative a question of G. Debs and J. Saint Raymond [Fund. Math. 204 (2009), no. 3], we construct a Borel ideal of rank >2>2 which does not contain an isomorphic copy of the ideal Fin3\text{Fin}^3.

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Cite

@article{arxiv.2109.01516,
  title  = {On a conjecture of Debs and Saint Raymond},
  author = {Adam Kwela},
  journal= {arXiv preprint arXiv:2109.01516},
  year   = {2025}
}