Friday, July 21th, 2017, 10.00-12.00
Aula S, Palazzo Campana, Università di Torino
Speaker: Yann Pequignot (University of California, Los Angeles)
Title: Sigma^1_2 sets and countable Borel chromatic numbers
Analytic sets enjoy a classical representation theorem based on wellfounded relations. I will explain a similar representation theorem for Sigma^1_2 sets due to Marcone. This can be used to answer negatively the primary outstanding question from (Kechris, Solecki and Todorcevic; 1999): the shift graph is not minimal among the graphs of Borel functions which have infinite Borel chromatic number.