{ "id": "math/0009080", "version": "v1", "published": "2000-09-07T20:18:27.000Z", "updated": "2000-09-07T20:18:27.000Z", "title": "A Note on Extensions of Infinitary Logic", "authors": [ "Saharon Shelah", "Jouko Väänänen" ], "categories": [ "math.LO" ], "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