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A Note on Extensions of Infinitary Logic

Saharon Shelah·Jouko Väänänen
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Abstract

We show that a strong form of the so called Lindstrom's Theorem fails to generalize to extensions of L_{kappa,omega} and L_{kappa,kappa}: For weakly compact kappa there is no strongest extension of L_{kappa,omega} with the (kappa,kappa)-compactness property and the Lowenheim-Skolem theorem down to kappa. With an additional set-theoretic assumption, there is no strongest extension of L_{kappa,kappa} with the (kappa,kappa)-compactness property and the Lowenheim-Skolem theorem down to <kappa.

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Saharon Shelah, Jouko Väänänen. 2000-09-07. A Note on Extensions of Infinitary Logic. https://arxiv.org/abs/math/0009080

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