Andreas Blass: The Tukey ordering and ultrafilters

Thursday, April 07, 2016, 4:00pm-5:30pm, at 2866 East Hall.
The Tukey ordering is a relation between directed partial orders. It was introduced for topological purposes, dealing with limits and accumulation points of nets. In recent years, it has been studied in the special situation where the directed sets are ultrafilters (directed by reverse inclusion), and connections have been found between the Tukey ordering and more traditional topics in ultrafilter theory. The first part of this talk will describe the Tukey ordering in general. Afterward, I’ll present some of the results and an open problem in the Tukey theory of ultrafilters.

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