27 January 2015
2:30 - 4:00   Martino Lupini
Polish groupoids and functorial complexity

We introduce the notion of functorial Borel complexity, aiming at capturing the complexity of classifying the objects of a category in an explicit and functorial way. We show that such a notion provides a finer distinction of functorial classification problems than the traditional perspective of Borel complexity theory. To establish such a result we develop the theory of Polish groupoids and their actions, building on previous works of Ramsay.