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Some initial segments of the Rudin-Keisler ordering
Published online by Cambridge University Press: 12 March 2014
Abstract
A 2-affable ultrafilter has only finitely many predecessors in the Rudin-Keisler ordering of isomorphism classes of ultrafilters over the natural numbers. If the continuum hypothesis is true, then there is an ℵ1-sequence of ultrafilters Dα such that the strict Rudin-Keisler predecessors of Dα are precisely the isomorphs of the Dβ's for β < α.
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- Copyright © Association for Symbolic Logic 1981
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