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Some initial segments of the Rudin-Keisler ordering

Published online by Cambridge University Press:  12 March 2014

Andreas Blass
Andreas Blass*
Affiliation:
University of Michigan, Ann Arbor, Michigan 48109
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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.

Type
Research Article
Information
The Journal of Symbolic Logic , Volume 46 , Issue 1 , March 1981 , pp. 147 - 157
Copyright
Copyright © Association for Symbolic Logic 1981

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References

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