# Jan Grebik: Borel selectors of Borel ideals (continued)

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