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Ultrafilter translations
Authors:Paolo Lipparini
Institution:(1) Dipartimento di Mathematica, Universitá di Roma (Tor Vergata), I-00133 Rome, Italy
Abstract:We develop a method for extending results about ultrafilters into a more general setting. In this paper we shall be mainly concerned with applications to cardinality logics. For example, assumingV=L, Gödel's Axiom of Constructibility, we prove that if lambda > ohgragr then the logic with the quantifier ldquothere existagr manyrdquo is (lambda,lambda)-compact if and only if either lambda is weakly compact or lambda is singular of cofinality<ohgragr. As a corollary, for every infinite cardinals lambda and mgr, there exists a (lambda,lambda)-compact non-(mgr,mgr)-compact logic if and only if either lambda<mgr orcflambda<cfmgr or lambda<mgr is weakly compact.Counterexamples are given showing that the above statements may fail, ifV=L is not assumed.However, without special assumptions, analogous results are obtained for the stronger notion of lambda,lambda]-compactness.
Keywords:primary 03C20  03C80  03C95  secondary 03E55  03E45  03C75
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