# Eventss

# Amitsur Symposium: Lev Glebsky - "Approximations of groups by finite and linear groups"

## Location:

and by unitary groups, respectively. I recall their definitions and discuss why those classes of groups are interesting. Then I consider approximations by other classes of groups and review some results, including rather recent ones by N. Nikolov, J. Schneider, A.Thom, https://arxiv.org/abs/1703.06092 .

If time permits I'll speak about stability and its relations with approximability.

# Amitsur Symposium: Arye Juhasz - "On the center of Artin groups"

## Location:

It is conjectured that all other irreducible Artin groups have trivial center. I prove this conjecture under a stronger assumption that not being spherical namely, if there is a standard generator which is not contained in any 3-generated spherical standard parabolic subgroup. The main tool is relative presentations of Artin groups.

# Amitsur Symposium: Yael Algom-Kfir - "The metric completion of an asymmetric metric space"

## Location:

eq d(y,x). The latter case is also incomplete: There exist Cauchy sequences that do not have a limit. We develop the theory of the completion of an asymmetric space and give lots of examples. Time permitting we will describe the case of Outer Space.

# Logic Seminar - Assaf Shani - "Borel equivalence relations and symmetric models"

## Location:

# HD-Combinatorics Special Day: "Quantum ergodicity and spectral theory with a discrete flavour" (organized by Elon Lindenstrauss and Shimon Brooks)

## Location:

9:00-10:50:

**Shimon Brooks**(Bar Ilan), "Delocalization of Graph Eigenfunctions"

14:00-15:50:

**Elon Lindenstrauss**(HUJI), "Quantum ergodicity on graphs and beyond"

See also the Basic Notions by Elon Lindenstrauss @ Ross 70 (16:30).

Abstract for morning session:

# NT&AG: Gal Porat (HUJI), "Induction and Restriction of $(\varphi,\Gamma)$-Modules"

## Location:

Joint work with Ehud de Shalit.

# T&G: Yaron Ostrover (Tel Aviv), Quantitative symplectic geometry in the classical phase space.

## Location:

# Logic Seminar - Antongiulio Fornasiero - "Generic solutions of exponential equations"

## Location:

dimension n.

If Schanuel Conjecture holds, under some natural conditions on V, we

show that, if V is defined over the rationals, there exists a in C^n

such that (a, exp(a)) is a generic point of V.

# HD-Combinatorics: Special day on sparsification (by Ilan Newman and Yuri Rabinovich)

## Location:

*Special day on sparsification*

Speakers:

**Ilan Newman**and

**Yuri Rabinovich**.

Part I: 10:30 - 12:30

Part II: 14:00 - 15:50

*Abstract for the day:*

Time permitting, we plan to discuss the following topics (in this order):

1.

* Additive Sparsification and VC dimension

* Multiplicative Sparsification

* Examples: cut weights, cut-dimension of L_1 metrics, general metrics,

and their high-dimensional analogues

2.

# IIAS outreach lecture: Prof. Gil Kalai "Sailing into High Dimensions"

## Lecturer:

## Location:

We will explain what high dimensions are, and describe some questions and answers in geometry and combinatorics of the high dimensional world.

# Basic Notions: Elon Lindenstrauss (HUJI) : Effective Equidistribution of closed orbits, property tau, and other applications

## Location:

# Elon Lindenstrauss (HUJI) - Effective Equidistribution and property tau

This is the second of two lectures on the paper Einseidler,, Margulis, Mohammadi and Venkatesh https://arxiv.org/abs/1503.05884. In this second lecture I will explain how the authors obtain using property tau (uniform spectral gap for arithmetic quotient) quantitaive equidistribution results for periodic orbits of maximal semisimple groups. Surprisingly, one can then use this theorem to establish property tau...

# No Basic notions seminar - deferred to 25.6

# CS Theory -- Erdős Lecture II: Counting contigency tables

## Lecturer:

## Location:

Contingency tables are matrices with fixed row and column sums. They are in natural correspondence with bipartite multi-graphs with fixed degrees and can also be viewed as integer points in transportation polytopes. Counting and random sampling of contingency tables is a fundamental problem in statistics which remains unresolved in full generality.

In the talk, I will review both asymptotic and MCMC approaches, and then present a new Markov chain construction which provably works for sparse margins. I conclude with some curious experimental results and conjectures. Read more about CS Theory -- Erdős Lecture II: Counting contigency tables