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Possible Size of an ultrapower of omega

Renling Jin, Saharon Shelah

arXiv, 1998

Abstract

Let omega be the first infinite ordinal (or the set of all natural numbers) with the usual order <. In section 1 we show that, assuming the consistency of a supercompact cardinal, there may exist an ultrapower of omega, whose cardinality is (1) a singular strong limit cardinal, (2) a strongly inaccessible cardinal. This answers two questions in [CK], modulo the assumption of supercompactness. In section 2 we construct several lambda-Archimedean ultrapowers of omega under some large cardinal assumptions. For example, we show that, assuming the consistency of a measurable cardinal, there may exist a lambda-Archimedean ultrapower of omega for some uncountable cardinal lambda. This answers a question in [KS], modulo the assumption of measurability.

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