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  1. Complexity of distances: Theory of generalized analytic equivalence relations.Marek Cúth, Michal Doucha & Ondřej Kurka - 2022 - Journal of Mathematical Logic 23 (1).
    We generalize the notion of analytic/Borel equivalence relations, orbit equivalence relations, and Borel reductions between them to their continuous and quantitative counterparts: analytic/Borel pseudometrics, orbit pseudometrics, and Borel reductions between them. We motivate these concepts on examples and we set some basic general theory. We illustrate the new notion of reduction by showing that the Gromov–Hausdorff distance maintains the same complexity if it is defined on the class of all Polish metric spaces, spaces bounded from below, from above, and from (...)
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  • Definability of groups in ℵ₀-stable metric structures.Itaï Ben Yaacov - 2010 - Journal of Symbolic Logic 75 (3):817-840.
    We prove that in a continuous ℵ₀-stable theory every type-definable group is definable. The two main ingredients in the proof are: 1. Results concerning Morley ranks (i.e., Cantor-Bendixson ranks) from [Ben08], allowing us to prove the theorem in case the metric is invariant under the group action; and 2. Results concerning the existence of translation-invariant definable metrics on type-definable groups and the extension of partial definable metrics to total ones.
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  • The model theory of modules of a C*-algebra.Camilo Argoty - 2013 - Archive for Mathematical Logic 52 (5-6):525-541.
    We study the theory of a Hilbert space H as a module for a unital C*-algebra ${\mathcal{A}}$ from the point of view of continuous logic. We give an explicit axiomatization for this theory and describe the structure of all the representations which are elementary equivalent to it. Also, we show that this theory has quantifier elimination and we characterize the model companion of the incomplete theory of all non-degenerate representations of ${\mathcal{A}}$ . Finally, we show that there is an homeomorphism (...)
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  • On perturbations of continuous structures.Itaï Ben Yaacov - 2008 - Journal of Mathematical Logic 8 (2):225-249.
    We give a general framework for the treatment of perturbations of types and structures in continuous logic, allowing to specify which parts of the logic may be perturbed. We prove that separable, elementarily equivalent structures which are approximately $aleph_0$-saturated up to arbitrarily small perturbations are isomorphic up to arbitrarily small perturbations. As a corollary, we obtain a Ryll-Nardzewski style characterisation of complete theories all of whose separable models are isomorphic up to arbitrarily small perturbations.
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  • ℵ 0 ‐categorical Banach spaces contain ℓp or c 0.Karim Khanaki - 2021 - Mathematical Logic Quarterly 67 (4):469-488.
    This paper has three parts. First, we establish some of the basic model theoretic facts about, the Tsirelson space of Figiel and Johnson [20]. Second, using the results of the first part, we give some facts about general Banach spaces. Third, we study model‐theoretic dividing lines in some Banach spaces and their theories. In particular, we show: (1) has the non independence property (NIP); (2) every Banach space that is ℵ0‐categorical up to small perturbations embeds c0 or () almost isometrically; (...)
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  • Model theoretic properties of metric valued fields.Itaï Ben Yaacov - 2014 - Journal of Symbolic Logic 79 (3):655-675.
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  • Almost Indiscernible Sequences and Convergence of Canonical Bases.Itaï Ben Yaacov, Alexander Berenstein & C. Ward Henson - 2014 - Journal of Symbolic Logic 79 (2):460-484.
    We give a model-theoretic account for several results regarding sequences of random variables appearing in Berkes and Rosenthal [12]. In order to do this,•We study and compare three notions of convergence of types in a stable theory: logic convergence, i.e., formula by formula, metric convergence (both already well studied) and convergence of canonical bases. In particular, we characterise א0-categorical stable theories in which the last two agree.•We characterise sequences that admit almost indiscernible sub-sequences.•We apply these tools to the theory of (...)
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  • A Topometric Effros Theorem.Itaï Ben Yaacov & Julien Melleray - forthcoming - Journal of Symbolic Logic:1-11.
    Given a continuous and isometric action of a Polish group G on an adequate Polish topometric space $(X,\tau,\rho )$ and $x \in X$, we find a necessary and sufficient condition for $\overline {Gx}^{\rho }$ to be co-meagre; we also obtain a criterion that characterizes when such a point exists. This work completes a criterion established in earlier work of the authors.
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