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SUMMARY:On the class of perfectly null sets and its transitive version - K
 orch\, M (Uniwersytet Warszawski)
DTSTART:20150826T130000Z
DTEND:20150826T133000Z
UID:TALK60464@talks.cam.ac.uk
CONTACT:42080
DESCRIPTION:The ideals of universally null sets (UN\, sets which are null 
 with respect  to  any  Borel  diffused  measure)  and  perfectly  meager  
 sets (PM\, sets which are meager when restricted to any perfect set) are b
 est  known  among  the  classes  of  special  subsets  of  the  real  line
 . Those two ideals were long considered to be somehow dual\, though some d
 ifferences were also known. P. Zakrzewski proved that two other earlier de
 fined classes of sets smaller then PM coincide and are dual to UN. Therefo
 re he proposed to call this class universally meager sets. The PM class wa
 s left without a counterpart\, and we try to define a class of sets which 
 may play the role of a dual class to PM and we also consider its transitiv
 e version. I will present some properties of those classes and give few im
 portant problems which are still open.\n
LOCATION:Seminar Room 1\, Newton Institute
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