Department of

# Mathematics

Seminar Calendar
for Logic Seminar events the year of Thursday, March 26, 2020.

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events for the
events containing

More information on this calendar program is available.
Questions regarding events or the calendar should be directed to Tori Corkery.
    February 2020            March 2020             April 2020
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
1    1  2  3  4  5  6  7             1  2  3  4
2  3  4  5  6  7  8    8  9 10 11 12 13 14    5  6  7  8  9 10 11
9 10 11 12 13 14 15   15 16 17 18 19 20 21   12 13 14 15 16 17 18
16 17 18 19 20 21 22   22 23 24 25 26 27 28   19 20 21 22 23 24 25
23 24 25 26 27 28 29   29 30 31               26 27 28 29 30



Tuesday, January 21, 2020

1:00 pm in 241 Altgeld Hall,Tuesday, January 21, 2020

#### Organizational meeting

Abstract: Just a short organizational meeting for Logic seminar and the MT/DST Seminar.

Tuesday, February 11, 2020

1:00 pm in 241 Altgeld Hall,Tuesday, February 11, 2020

#### The Borel complexity of quotient groups

###### Joshua Frisch (Caltech Math)

Abstract: The theory of Borel equivalence relations gives us rigorous methods to says when one classification problem/equivalence relation is more "complicated" than another. Given a countable group it's outer-automorphism group naturally has the structure of a borel equivalence relation. Motivated by this example, in this talk I will give a brief introduction to the theory of countable borel equivalence relations, describe some previously known connections with the theory of groups and, finally, describe a new new result explaining exactly how complicated the Borel complexity of quotient groups (which generalize outer-automorphism groups) can be. This is joint work with Forte Shinko.

Tuesday, March 24, 2020

1:00 pm in https://illinois.zoom.us/j/249415194,Tuesday, March 24, 2020

#### Borel structures on the space of left orderings

###### Filippo Calderoni (UIC Math)

Abstract: In this talk I will present some recent results on left-orderable groups and their interplay with descriptive set theory. We shall discuss how Borel classification can be used to analyze the space of left-orderings of a given countable group modulo the conjugacy action. In particular we shall see that if G is a countable nonabelian free group, then the conjugacy relation on its space of left orderings is a universal countable Borel equivalence relation. This is joint work with A. Clay.

Friday, April 3, 2020

3:00 pm in https://illinois.zoom.us/j/521113604,Friday, April 3, 2020

#### A dynamical obstruction for classification by actions of TSI Polish groups

###### Aristotelis Panagiotopoulos (Caltech Math)

Abstract: A big part of mathematical activity revolves around classification problems. However, not every classification problem has a satisfactory solution, and some classification problems are more complicated than others. Dynamical properties such as generic ergodicity and turbulence are crucial in the development of a rich complexity theory for classification problems. In this talk we will review some of the existing anti-classification techniques and we will introduce a new obstruction for classification by orbit equivalence relations of TSI Polish groups; a topological group is TSI if it admits a compatible two side invariant metric. We will then show that the Wreath product of any two non-compact subgroups of $S_{\infty}$ admits an action whose orbit equivalence relation is generically ergodic with respect to orbit equivalence relations of TSI group actions.
This is joint work with Shaun Allison.

Friday, April 17, 2020

4:00 pm in ??? Altgeld Hall,Friday, April 17, 2020

#### To Be Announced

###### Meng-Che (Turbo) Ho (Purdue University)

Tuesday, April 21, 2020

1:00 pm in 241 Altgeld Hall,Tuesday, April 21, 2020