# Ultrafilters in Topology

I have seen the use of ultrafilters in topology to prove Tychonoff's theorem. In fact, this is the only application of ultrafilters in topology I have been able to find so far.

Are there any other applications of ultrafilters to topology?

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The Stone-Cech compactification can be constructed using ultrafilters. – Martin Jan 25 at 9:37
There's a 2010 survey book: ams.org/bookstore-getitem/item=CONM-530 – alancalvitti Jan 25 at 14:40