[Settfa] Tuesday 29/10, Maciej Malicki

[kubis at math.cas.cz]

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 Tuesday 29th October, 11:00am 
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 Speaker:Maciej Malicki, Warsaw School of Economics, Poland
 Title: On Polish groups admitting non-essentially countable actions

 Abstract  

 A. Kechris proved that every orbit equivalence relation induced by a continuous action of a locally compact Polish group on a Polish space is essentially countable, i.e., it is Borel reducible to an orbit equivalence relation with countable classes. It is a long-standing open question whether the converse holds. We answer this question positively for the class of all Polish groups that embed in the isometry group of a locally compact metric space. This class contains all non-Archimedean Polish groups, for which we provide an alternative proof based on a new criterion for non-essential countability. This is joint work with A. Kechris, J. Zielinski and A. Panagiotopoulos.

 For more information see the seminar web page at 
 https://calendar.math.cas.cz/set-theory-and-analysis-actual .