Abstract

We continue the study of Rosenthal families initiated by Damian Sobota. We show that every Rosenthal filter is the intersection of a finite family of ultrafilters that are pairwise incomparable in the Rudin-Keisler partial ordering of ultrafilters. We introduce a property of filters, called an \-filter, properly between a selective filter and a \-filter. We prove that every \-ultrafilter is a Rosenthal family. We prove that it is consistent with ZFC to have uncountably many \-ultrafilters such that any intersection of finitely many of them is a Rosenthal filter.