Dear all,

The seminar meets on Wednesday October 25th at 11:00 in the Institute of

Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.

Program: Jan Grebik — Borel selectors of Borel ideals (continued)

We present a result that there is an F_sigma ideal without Borel

selector and deduce that Galvin’s lemma does not have a “Borel proof.”

We also show that Nash-Williams theorem has a “Borel proof” and

therefore Galvin’s lemma is intrinsically more complex than

Nash-Williams theorem.

Best,

David