Department of

# Mathematics

Seminar Calendar
for events the day of Wednesday, November 28, 2018.

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events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
     October 2018          November 2018          December 2018
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1  2  3  4  5  6                1  2  3                      1
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30 31


Wednesday, November 28, 2018

3:00 pm in 241 Altgeld Hall,Wednesday, November 28, 2018

#### $\ell^2$ Betti numbers of countable Borel equivalence relations: Part 3

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

Abstract: We will continue to discuss Gaboriau's 2002 paper "Invariants $\ell^2$ de relations d'équivalence et de groupes" from a descriptive set-theoretic point of view. In this second talk, we will discuss Borel fields of sets and structures (in particular, simplicial complexes and Hilbert spaces) over a countable Borel equivalence relation, and how to measure their "Borel cardinality" using Tarski's theory of cardinal algebras.

4:00 pm in 245 Altgeld Hall,Wednesday, November 28, 2018

#### Random number theory

###### Carl Pomerance (Dartmouth College)

Abstract: No, this is not a talk about random numbers! Rather, we discuss the role of randomness in number theory, from Euler to the present. We'll visit the probabilistic background of Fermat's Last Theorem, the ABC conjecture, the Prime Number Theorem, the Riemann Hypothesis, Goldbach's Conjecture, and the Twin-Prime Conjecture, among other famous problems and results. Randomness has had a profound influence in computational number theory. In combinatorial number theory, the Probabilistic Method (best known in graph theory and combinatorics) is used to prove the existence of strange structures. In algebraic number theory the probability-based Cohen-Lenstra heuristics lead us to conjectures (and theorems too) about the distribution of algebraic number fields. We close with the famous Covering Congruences problem of Paul Erdös, which was recently settled with probabilistic tools.