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arXiv · 2605.13683

O-minimal open core is not an elementary property

Alexi Block Gorman·Esther Elbaz Saban
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Abstract

Given a structure $\mathcal{M}$ with a definable topology, its open core is a structure defined on the same universe whose language consists of all open sets of all arities definable in $\mathcal{M}$. In response to questions raised by Dolich, Miller, and Steinhorn in their early work on open core, we prove that having an o-minimal open core is not an elementary property. In particular, we construct an expansion of the structure $(\mathbb{Q},<)$ that has an o-minimal open core, but some of its elementary superstructures do not.

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Alexi Block Gorman, Esther Elbaz Saban. 2026-05-13. O-minimal open core is not an elementary property. https://arxiv.org/abs/2605.13683

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