On the cofinality of ultrapowers

Authors
Blass, A Mildenberger, H
Citation
A. Blass et H. Mildenberger, On the cofinality of ultrapowers, J SYMB LOG, 64(2), 1999, pp. 727-736
Citations number
11
Categorie Soggetti
Mathematics
Journal title
JOURNAL OF SYMBOLIC LOGIC
ISSN journal
00224812 → ACNP
Volume
64
Issue
2
Year of publication
1999
Pages
727 - 736
Database
ISI
SICI code
0022-4812(199906)64:2<727:OTCOU>2.0.ZU;2-F
Abstract
We prove some restrictions on the possible cofinalities of ultrapowers of t he natural numbers with respect to ultrafilters on the natural numbers. The restrictions involve three cardinal characteristics of the continuum, the splitting number s, the unsplitting number r. and the groupwise density num ber g. We also prove some related results for reduced powers with respect t o filters other than ultrafilters.