Department of

Mathematics


Seminar Calendar
for Descriptive Set Theory Seminar events the year of Friday, September 14, 2018.

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More information on this calendar program is available.
Questions regarding events or the calendar should be directed to Tori Corkery.
     August 2018           September 2018          October 2018    
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                        30                                         

Friday, January 26, 2018

4:00 pm in 345 Altgeld Hall,Friday, January 26, 2018

First order expansions of the ordered real additive group — Part II

Philipp Hieronymi (UIUC Math)

Abstract: This is a (hopefully self-contained) continuation of Erik's talk from Tuesday. I will discuss in more detail expansions of the ordered real additive group that are of type B (ie expansions of $(\mathbb{R},<,+)$ that define an order $(D,\prec)$ of order-type $\omega$ whose underlying set $D$ is somewhere dense in $\mathbb R$). In many (all?) type B structures 0-definability is equivalent to recognizablility by a Buechi automaton. Therefore results about the definable sets in type B structures imply results about sets recognizable by such automata. In this talk I will focus on our current research on continuous definable functions in type B structures, and I will discuss how it connects to results in computer science by Chaudhuri, Sankaranarayanan and Vardi.

Friday, February 2, 2018

4:00 pm in 345 Altgeld Hall,Friday, February 2, 2018

On "A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets" by Achille and Berarducci

Elliot Kaplan (UIUC Math)

Abstract: I will discuss the paper "A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets" by Alessandro Achille and Alessandro Berarducci [arXiv]. In this paper, they compare the definable homotopy groups of a space $X$ definable in an o-minimal structure (denoted $\pi_n(X)^\mathrm{def}$) with the (usual) homotopy groups of the quotient $X/E$, where $E$ is a certain kind of type-definable equivalence relation on $X$. Under certain assumptions, these groups are actually isomorphic. These types of quotients were first studied by Pillay in the case that $X$ is actually a definable group. This is the first talk that I will give on this paper.

Friday, February 9, 2018

4:00 pm in 345 Altgeld Hall,Friday, February 9, 2018

More on ``A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets'' by Achille and Berarducci

Elliot Kaplan (UIUC Math)

Abstract: I will continue to discuss the paper ``A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets'' by Alessandro Achille and Alessandro Berarducci [arXiv]. I will sketch the proofs of the two main theorems, in which they show that under certain conditions, the definable homotopy groups of a space $X$ definable in an o-minimal structure are isomorphic to the (usual) homotopy groups of the quotient of $X$ by a certain kind of type-definable equivalence relation $E$. This is the second talk on this paper.

Friday, February 16, 2018

4:00 pm in 345 Altgeld Hall,Friday, February 16, 2018

Canceled

Tuesday, February 20, 2018

4:00 pm in 243 Altgeld Hall,Tuesday, February 20, 2018

A pointwise ergodic theorem for quasi-pmp graphs

Anush Tserunyan (UIUC Math)

Abstract: We prove a pointwise ergodic theorem for quasi-pmp locally countable graphs, which states that the global condition of ergodicity amounts to locally approximating the means of $L^1$-functions via increasing subgraphs with finite connected components. The pmp version of this theorem was first proven by R. Tucker-Drob using probabilistic methods. Our proof is different: it is constructive and applies more generally to quasi-pmp graphs. Among other things, it involves introducing a graph invariant and a simple method of exploiting nonamenability. The non-pmp setting additionally requires a new gadget for analyzing the interplay between the underlying cocycle and the graph.

Friday, February 23, 2018

4:00 pm in 345 Altgeld Hall,Friday, February 23, 2018

"On dp-minimal ordered structures" by P. Simon (part 1)

Travis Nell (Illinois Math)

Abstract: This is an introductory talk to "On dp-minimal ordered structures" by P. Simon [arXiv].

Friday, March 2, 2018

4:00 pm in 1 Illini Hall,Friday, March 2, 2018

"On dp-minimal ordered structures" by P. Simon (part 2)

Alexi Block Gorman (Illinois Math)

Abstract: We continue reading through "On dp-minimal ordered structures" by P. Simon [arXiv].

Friday, March 9, 2018

4:00 pm in 345 Altgeld Hall,Friday, March 9, 2018

"On dp-minimal ordered structures" by P. Simon (part 3)

Alexi Block Gorman (Illinois Math)

Abstract: We continue reading through "On dp-minimal ordered structures" by P. Simon [arXiv].

Friday, March 16, 2018

4:00 pm in 345 Altgeld Hall,Friday, March 16, 2018

Cancelled

Friday, March 30, 2018

4:00 pm in 345 Altgeld Hall,Friday, March 30, 2018

Dp-minimal expansions of $(\mathbb{Q},<,+)$

Erik Walsberg (Illinois Math)

Abstract: I will use P. Simon's result to relate dp-minimal expansions of $(\mathbb{Q},<,+)$ to o-minimal expansions of $(\mathbb{R},<,+)$, I will also describe a nice application of the Pettis lemma to o-minimality.

Friday, April 6, 2018

4:00 pm in 345 Altgeld Hall,Friday, April 6, 2018

Dp-minimal expansions of $(\mathbb{Q},<,+)$ (continued)

Erik Walsberg (Illinois Math)

Abstract: I will use P. Simon's result to relate dp-minimal expansions of $(\mathbb{Q},<,+)$ to o-minimal expansions of $(\mathbb{R},<,+)$, I will also describe a nice application of the Pettis lemma to o-minimality.

Tuesday, April 10, 2018

1:00 pm in 345 Altgeld Hall,Tuesday, April 10, 2018

"On dp-minimal ordered structures" by P. Simon (part 4)

Elliot Kaplan (Illinois Math)

Abstract: We continue through "On dp-minimal ordered structures" by P. Simon [arXiv].

Friday, April 20, 2018

4:00 pm in 345 Altgeld Hall,Friday, April 20, 2018

Polishable Borel equivalence relations

Sławomir Solecki (Cornell)

Abstract: We introduce the notion of Polishable equivalence relations. This class of equivalence relations contains all orbit equivalence relations induced by Polish group actions and is contained in the class of idealistic equivalence relations of Kechris and Louveau. We show that each orbit equivalence relation induced by a Polish group action admits a canonical transfinite sequence of Polishable equivalence relations approximating it. The proof involves establishing a lemma, which may be of independent interest, on stabilization of increasing $\omega_1$-sequences of completely metrizable topologies.

Thursday, September 6, 2018

12:00 pm in 241 Altgeld Hall,Thursday, September 6, 2018

On "Closed subgroups generated by generic measure automorphisms" by S. Solecki, Part 1

Dakota Ihli (UIUC Math)

Abstract: We will read through this paper.

Wednesday, September 12, 2018

3:00 pm in 241 Altgeld Hall,Wednesday, September 12, 2018

On "Closed subgroups generated by generic measure automorphisms" by S. Solecki, Part 2

Dakota Ihli (UIUC Math)

Abstract: We will sketch the proof of the main result in this paper.

Wednesday, September 19, 2018

3:00 pm in 241 Altgeld Hall,Wednesday, September 19, 2018

On "Closed subgroups generated by generic measure automorphisms" by S. Solecki, Part 3

Dakota Ihli (UIUC Math)

Abstract: We will sketch the proof of the main result in this paper.

Wednesday, September 26, 2018

3:00 pm in 241 Altgeld Hall,Wednesday, September 26, 2018

A combinatorial proof of the classical pointwise ergodic theorem

Jenna Zombach (UIUC Math)