Approximate isomorphism of randomization pairs

James Hanson; Tomás Ibarlucía

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arXiv · 2202.04151

Approximate isomorphism of randomization pairs

James Hanson·Tomás Ibarlucía

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Abstract

We study approximate $\aleph_0$-categoricity of theories of beautiful pairs of randomizations, in the sense of continuous logic. This leads us to disprove a conjecture of Ben Yaacov, Berenstein and Henson, by exhibiting $\aleph_0$-categorical, $\aleph_0$-stable metric theories $Q$ for which the corresponding theory $Q_P$ of beautiful pairs is not approximately $\aleph_0$-categorical, i.e., has separable models that are not isomorphic even up to small perturbations of the smaller model of the pair. The theory $Q$ of randomized infinite vector spaces over a finite field is such an example. On the positive side, we show that the theory of beautiful pairs of randomized infinite sets is approximately $\aleph_0$-categorical. We also prove that a related stronger property, which holds in that case, is stable under various natural constructions, and formulate our guesswork for the general case.

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BibTeX RIS

James Hanson, Tomás Ibarlucía. 2022-02-08. Approximate isomorphism of randomization pairs. https://arxiv.org/abs/2202.04151

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