Peter Krautzberger on the web

Red workbook, p8


red workbook, p8
Red Workbook, p.8


partial Translation


More wonderful stuff about thick, piecewise syndetics, and central sets.

The lemma tells us that pws could be called “almost thick” – a finite set of translations is enough to make a pws set thick. The proposition on the other hand tells us that pws is surprisingly close to being central – just one translation! (just keep in mind they are very much not the same notion). In addition, such a translation happens very, very frequently (a syndetic set!).

Somehow, I find this to be a lot of fun even if it’s not particularly surprising – minimal idempotent ultrafilters are just so incredibly rich.