# David Fernández: Strongly summable ultrafilters and union ultrafilters are not the same thing

21/June/2013, 13:30–15:00
Fields institute,Room 210

Speaker: David J. Fernández Bretón

Title: Strongly summable ultrafilters and union ultrafilters are not the same thing

Abstract: This is, in some sense, a continuation of my previous talk (though of course self-contained). So I will introduce strongly summable ultrafilters, union ultrafilters, and additive isomorphisms, and then I will proceed with the construction (assuming cov(M)=c) of a strongly summable ultrafilter (on the Boolean group) that is not additively isomorphic to any union ultrafilter.