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  1. Destructibility and axiomatizability of Kaufmann models.Corey Bacal Switzer - 2022 - Archive for Mathematical Logic 61 (7):1091-1111.
    A Kaufmann model is an \(\omega _1\) -like, recursively saturated, rather classless model of \({{\mathsf {P}}}{{\mathsf {A}}}\) (or \({{\mathsf {Z}}}{{\mathsf {F}}} \) ). Such models were constructed by Kaufmann under the combinatorial principle \(\diamondsuit _{\omega _1}\) and Shelah showed they exist in \(\mathsf {ZFC}\) by an absoluteness argument. Kaufmann models are an important witness to the incompactness of \(\omega _1\) similar to Aronszajn trees. In this paper we look at some set theoretic issues related to this motivated by the seemingly (...)
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  • Fermat’s last theorem proved in Hilbert arithmetic. I. From the proof by induction to the viewpoint of Hilbert arithmetic.Vasil Penchev - 2021 - Logic and Philosophy of Mathematics eJournal (Elsevier: SSRN) 13 (7):1-57.
    In a previous paper, an elementary and thoroughly arithmetical proof of Fermat’s last theorem by induction has been demonstrated if the case for “n = 3” is granted as proved only arithmetically (which is a fact a long time ago), furthermore in a way accessible to Fermat himself though without being absolutely and precisely correct. The present paper elucidates the contemporary mathematical background, from which an inductive proof of FLT can be inferred since its proof for the case for “n (...)
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  • Models of expansions of equation image with no end extensions.Saharon Shelah - 2011 - Mathematical Logic Quarterly 57 (4):341-365.
    We deal with models of Peano arithmetic. The methods are from creature forcing. We find an expansion of equation image such that its theory has models with no end extensions. In fact there is a Borel uncountable set of subsets of equation image such that expanding equation image by any uncountably many of them suffice. Also we find arithmetically closed equation image with no ultrafilter on it with suitable definability demand. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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  • Unifying the model theory of first-order and second-order arithmetic via WKL 0 ⁎.Ali Enayat & Tin Lok Wong - 2017 - Annals of Pure and Applied Logic 168 (6):1247-1283.
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  • A note on standard systems and ultrafilters.Fredrik Engström - 2008 - Journal of Symbolic Logic 73 (3):824-830.
    Let (M, X) ⊨ ACA₀ be such that P X, the collection of all unbounded sets in X, admits a definable complete ultrafilter and let T be a theory extending first order arithmetic coded in X such that M thinks T is consistent. We prove that there is an end-extension N ⊨ T of M such that the subsets of M coded in N are precisely those in X. As a special case we get that any Scott set with a (...)
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