2019 Dec 16

# Combinatorics: Orit Raz (HUJI)

10:00am to 12:00pm

## Location:

C-400, CS building

Combinatorics Seminar HUJI

When: Monday Dec 16, 10:00-11:45
Where: C-400, CS building

Speaker: Orit Raz (HUJI)

Title: Dense graphs have rigid parts

Abstract:
2019 Dec 02

# Combinatorics: Boaz Slomka (Open U.)

10:00am to 12:00pm

## Location:

C-400, CS building

Speaker: Boaz Slomka (Open U.)

Abstract:
A long-standing open problem, known as Hadwiger’s covering problem, asks what is the smallest natural number N(n) such that every convex body in R^n can be covered by a union of the interiors of N(n) of its translates.

In this talk, I will discuss some history of this problem and its close relatives, and present more recent results, including a general upper bound for N(n).
2019 Dec 09

# Combinatorics: Ilan Newman (Haifa)

10:00am to 12:00pm

## Location:

C-400, CS building

Speaker: Ilan Newman (Haifa)

Title:  Some recent results on sublinear algorithms for graph related properties

Abstract:
I will describe property testing of (di)graph properties in bounded degree graph models, and talk about a characterization of the 1-sided error testable monotone graph properties and the 1-sided error testable hereditary graph properties in this model. I will introduce the notion of configuration-free properties and talk about some graph theoretic open problems.
2019 Nov 04

# Combinatorics: Zlil Sela (HUJI) "Combinatorics and geometry in non-commutative algebraic geometry"

10:00am to 12:00pm

## Location:

CS building, C-400
Title: Combinatorics and geometry in non-commutative algebraic geometry
Abstract:
2019 Nov 14

# Groups & Dynamics seminar: Gil Goffer (Weizmann): "Conjugacy and Dynamics in Tree Almost-Automorphisms."

10:00am to 11:00am

## Location:

Ross 70
Abstract: When are two elements in a given group conjugate? We solve this problem for the group of tree almost-automorphisms. These are homeomorphisms of the tree boundary which locally look like tree automorphisms. The solution is tied with the dynamics of the group action on the tree boundary. This work is joint with W. Lederle.
2019 Nov 12

# Weikun He (HUJI) - Spectral gap of the action of subgroups of SL(d,Z) on torus following Bekka and Guivarch

12:00pm to 1:00pm

2019 Dec 24

# Genadi Levin (HUJI) - The Lyapunov exponent of rational maps

12:00pm to 1:00pm

2019 Dec 05

# Colloquium: Yoel Groman (HUJI) - Floer homology of the magnetic cotangent bundle

2:30pm to 3:30pm

## Location:

Manchester Building (Hall 2), Hebrew University Jerusalem

Hamiltonian Floer cohomology was invented by A. Floer to prove the Arnold conjecture: a Hamiltonian diffemorphism of a closed symplectic manifold has at least as many periodic orbits as the sum of the Betti numbers. A variant called Symplectic cohomology was later defined for certain non compact manifolds, including the  cotangent bundle of an arbitrary closed smooth manifold. The latter is the setting for classical mechanics of constrained systems.

2019 Nov 06

# Logic Seminar - Itay Kaplan

11:00am to 1:00pm

## Location:

Ross building - Room 63
On distal and co-distal types

I will define the notions described in the title, and ask if they are equivalent. I will present a proof showing that they are in case the theory is NIP. The proof is essentially the proof of the fact that the lack of distality is witnessed by a sequence of singletons by Pierre Simon’s.
2019 Nov 18

# NT Seminar - Zev Rosengarten

2:30pm to 3:30pm

## Location:

Ross 70
Title: Mordell-Lang and Integral Points on Abelian Varieties in Characteristic p
2019 Nov 11

# NT Seminar - Katharina Hübner

2:30pm to 3:30pm

## Location:

Ross 70
Title: The tame site
2019 Nov 04

# NT & AG Lunch: Michael Temkin, "Resolution of singularities"

Repeats every week every Monday until Sun Dec 15 2019 .
1:00pm to 2:00pm

1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm

## Location:

Mathematics, Faculty Lounge
This semester will be devoted to resolution of singularities -- a process that modifies varieties at the singular locus so that the resulting variety becomes smooth. For many years this topic had the reputation of very technical and complicated, though rather elementary.
In fact, the same resolution algorithm can be described in various settings, including schemes, algebraic varieties or complex analytic spaces.
2019 Dec 10

# Boris Solomyak (BIU) Hoelder regularity for the spectrum of translation flows

2:00pm to 3:00pm

Abstract: We consider generic translation flows corresponding to Abelian differentials on flat surfaces of genus $g\ge 2$. These flows are weakly mixing by the Avila-Forni theorem. Recently Forni obtained Hoelder estimates on spectral measures for almost all translation flows, following earlier work by Bufetov and myself in genus two. Combining Forni's idea with our methods, we extended our proof to the case of arbitrary genus $g\ge 2$. It is based on a vector form of the Erd\H{o}s-Kahane argument, which I will try to explain.
This is a joint work with A. Bufetov.
2019 Oct 30

# Logic Seminar - Eugenio Colla

11:00am to 1:00pm

## Location:

Ross 63
Model-theoretic proofs of partition theorems for semigroups.

Abstract:
Partition theorems have the following form. Let "regular" be some notion for a structure S; theorem: for every finite partition of S there is a "regular" set inside a cell of the partition.
2019 Nov 19

# Amitay Kamber (HUJI): Invariant Random Subgroups and Essential Girth of Ramanujan graphs, following Abert, Glasner, and Virag

12:00pm to 1:00pm