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arXiv · 2602.23340

Combinatorial Properties of the Raisonnier Filter

Spyridon Dialiatsis·Yurii Khomskii
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Abstract

The Raisonnier Filter is a combinatorial object isolated by Jean Raisonnier in order to simplify Shelah's proof that if all $\boldsymbol{\Sigma}^1_3$ sets are Lebesgue-measurable then there is an inner model with an inaccessible cardinal. In this paper, we study the combinatorics of a general version of the Raisonnier filter, with an eye to potential applications in descriptive set theory. Among the most interesting of our results is a partial converse to Raisonnier's theorem, which can be used to provide a new characterisation of the statement "all $\boldsymbol{\Sigma}^1_2$ sets are measurable". We also introduce an ideal on the Cantor Space induced by the Raisonnier filter and study its cardinal characteristics, connecting them to the well-known characteristics in Cicho\'n's Diagram.

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Spyridon Dialiatsis, Yurii Khomskii. 2026-02-26. Combinatorial Properties of the Raisonnier Filter. https://arxiv.org/abs/2602.23340

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