David Fernandez Breton: All that there is to know about gruff ultrafilters, II

Wednesday, September 23, 2015 — 16:00 to 17:30 — 3096 East Hall

An ultrafilter on the rational numbers is gruff if it has a base of perfect (this is, closed and without isolated points) sets. This definition, as well as the (still open) question of whether these objects exist, are due to van Douwen. We will present a completion of last time’s almost proof that b=c implies the existence of a gruff ultrafilter, and afterwards we will show that in Miller’s model there are gruff ultrafilters as well.

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