Department of

# Mathematics

Seminar Calendar
for events the day of Wednesday, October 30, 2019.

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events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
    September 2019          October 2019          November 2019
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1  2  3  4  5  6  7          1  2  3  4  5                   1  2
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Wednesday, October 30, 2019

3:00 pm in 241 Altgeld Hall,Wednesday, October 30, 2019

#### On uniform ergodic decomposition

###### Ruiyuan (Ronnie) Chen (UIUC Math)

Abstract: We will prove Farrell–Varadarajan's uniform ergodic decomposition theorem for countable Borel equivalence relations. The proof we give is based on using the Becker–Kechris comparability lemma to construct uniform conditional probability functions for Borel sets.

4:00 pm in 447 Altgeld,Wednesday, October 30, 2019

#### A Case for Étale Cohomology

###### Justin Kelm (Illinois Math)

Abstract: This talk will serve as an introduction to étale cohomology. In particular, I will focus on the shortcomings of Zariski cohomology, why étale maps are a good algebro-geometric substitute for the notion of a "covering map" or "local" diffeomorphism, the technology that étale cohomlogy is built out of, and a basic computation or two that should illuminate why étale cohomology should give rise to a useful Weil cohomology theory.