caa a22 4500 388039272 CHVBK 20180307125016.0 cr unu---uuuuu 161130e199806 xx s 000 0 eng 10.2307/2586852 doi S0022481200015103 pii (NATIONALLICENCE)cambridge-10.2307/2586852 The Rudin-Blass ordering of ultrafilters [Elektronische Daten] We discuss the finite-to-one Rudin-Keisler ordering of ultrafilters on the natural numbers, which we baptize the Rudin-Blass ordering in honour of Professor Andreas Blass who worked extensively in the area. We develop and summarize many of its properties in relation to its bounding and dominating numbers, directedness, and provide applications to continuum theory. In particular, we prove in ZFC alone that there exists an ultrafilter with no Q-point below in the Rudin-Blass ordering. Copyright © Association for Symbolic Logic 1998 Laflamme Claude Department of Mathematics and Statistics, University of Calgary, Calgary, Alberta, Canada T2N 1N4, E-mail: laflamme@acs.ucalgary.ca Zhu Jian-Ping Versus Technologies Inc., 181 Bay Street, Suite 3810, Toronto, Canada M5J 2T3, E-mail: jzhu@tradeit.com The Journal of Symbolic Logic Cambridge University Press 63/2(1998-06), 584-592 0022-4812 63:2<584 1998 63 JSL https://doi.org/10.2307/2586852 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.2307/2586852 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Laflamme Claude Department of Mathematics and Statistics, University of Calgary, Calgary, Alberta, Canada T2N 1N4, E-mail: laflamme@acs.ucalgary.ca NATIONALLICENCE 700 1- Zhu Jian-Ping Versus Technologies Inc., 181 Bay Street, Suite 3810, Toronto, Canada M5J 2T3, E-mail: jzhu@tradeit.com NATIONALLICENCE 773 0- The Journal of Symbolic Logic Cambridge University Press 63/2(1998-06), 584-592 0022-4812 63:2<584 1998 63 JSL CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge