2016 Feb 24

# Topology & geometry, Mikhail Katz (Bar Ilan University), "Determinantal variety and bi-Lipschitz equivalence"

11:00am to 12:45pm

## Location:

Ross building, Hebrew University (Seminar Room 70A)
Abstract: The unit circle viewed as a Riemannian manifold has diameter (not 2 but rather) π, illustrating the difference between intrinsic and ambient distance. Gromov proceeded to erase the difference by pointing out that when a Riemannian manifold is embedded in L∞, the intrinsic and the ambient distances coincide in a way that is as counterintuitive as it is fruitful. Witness the results of his 1983 Filling paper.
2015 Dec 02

# Topology & geometry: Pavel Paták (HUJI), "Homological non-embeddability and a qualitative topological Helly-type theorem"

11:00am to 12:45pm

## Location:

Ross building, Hebrew University (Seminar Room 70A)
Abstract: The classical theorem of Van Kampen and Flores states that the k-dimensional skeleton of (2k+2)-dimensional simplex cannot be embedded into R2k. We present a version of this theorem for chain maps and as an application we prove a qualitative topological Helly-type theorem. If we define the Helly number of a finite family of sets to be one if all sets in the family have a point in common and as the largest size of inclusion-minimal subfamily with empty intersection otherwise, the theorem can be stated as follows:
2016 Feb 17

# Menachem Magidor 70th Birthday Conference

Wed, 17/02/2016 (All day) to Fri, 19/02/2016 (All day)

2016 Nov 17

# Groups and dynamics: Arie Levit

10:30am to 11:30am

## Location:

Ross 70
Speaker: Arie Levit Weizmann Institute Title: Local rigidity of uniform lattices Abstract: A lattice is topologically locally rigid (t.l.r) if small deformations of it are isomorphic lattices. Uniform lattices in Lie groups were shown to be t.l.r by Weil [60']. We show that uniform lattices are t.l.r in any compactly generated topological group.
2016 Dec 15

# Groups and dynamics: Yair Hartman (Northwestern) - Percolation, Invariant Random Subgroups and Furstenberg Entropy

10:30am to 11:30am

## Location:

Ross 70
Abstract: In this talk I'll present a joint work with Ariel Yadin, in which we solve the Furstenberg Entropy Realization Problem for finitely supported random walks (finite range jumps) on free groups and lamplighter groups. This generalizes a previous result of Bowen. The proof consists of several reductions which have geometric and probabilistic flavors of independent interests. All notions will be explained in the talk, no prior knowledge of Invariant Random Subgroups or Furstenberg Entropy is assumed.
2015 Dec 31

# Groups & dynamics: Thang Neguyen (Weizmann) - Rigidity of quasi-isometric embeddings

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)
To every topological group, one can associate a unique universal minimal flow (UMF): a flow that maps onto every minimal flow of the group. For some groups (for example, the locally compact ones), this flow is not metrizable and does not admit a concrete description. However, for many "large" Polish groups, the UMF is metrizable, can be computed, and carries interesting combinatorial information. The talk will concentrate on some new results that give a characterization of metrizable UMFs of Polish groups. It is based on two papers, one joint
2016 Mar 31

# Groups & dynamics: Paul Nelson (ETH) - Quantum variance on quaternion algebras

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)
To every topological group, one can associate a unique universal minimal flow (UMF): a flow that maps onto every minimal flow of the group. For some groups (for example, the locally compact ones), this flow is not metrizable and does not admit a concrete description. However, for many "large" Polish groups, the UMF is metrizable, can be computed, and carries interesting combinatorial information. The talk will concentrate on some new results that give a characterization of metrizable UMFs of Polish groups. It is based on two papers, one joint
2016 Dec 01

# Groups and dynamics: Masaki Tsukamoto (lecture 1)

10:30am to 11:30am

## Location:

Ross 70
INTRODUCTION TO MEAN DIMENSION AND THE EMBEDDING PROBLEM OF DYNAMICAL SYSTEMS (Part 1)
2016 Nov 24

# Groups and dynamics- Oren Becker

10:30am to 11:30am

## Location:

Ross 70
Speaker: Oren Becker Title: Locally testable groups Abstract: Arzhantseva and Paunescu [AP2015] showed that if two permutations X and Y in Sym(n) nearly commute (i.e. XY is close to YX), then the pair (X,Y) is close to a pair of permutations that really commute.
2016 Dec 22

# Groups and dynamics: Masaki Tsukamoto (lecture 3)

10:30am to 11:30am

Ross 70
2016 Jan 07

# Groups & dynamics: Mark Shusterman (TAU) - Ranks of subgroups in boundedly generated groups

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)
To every topological group, one can associate a unique universal minimal flow (UMF): a flow that maps onto every minimal flow of the group. For some groups (for example, the locally compact ones), this flow is not metrizable and does not admit a concrete description. However, for many "large" Polish groups, the UMF is metrizable, can be computed, and carries interesting combinatorial information. The talk will concentrate on some new results that give a characterization of metrizable UMFs of Polish groups. It is based on two papers, one joint
2016 Dec 08

# Groups and dynamics: Masaki Tsukamoto (lecture 2)

10:30am to 11:30am

Ross 70
2016 Dec 29

# Groups and dynamics: Masaki Tsukamoto (lecture 4)

10:30am to 11:30am

Ross 70
2016 Mar 03

# Groups & dynamics: Karim Adiprasito (HUJI) - Contractible manifolds, hyperbolicity and the fundamental pro-group at infinity

10:00am to 11:00am

## Location:

Ross building, Hebrew University of Jerusalem, (Room 70)
To every topological group, one can associate a unique universal minimal flow (UMF): a flow that maps onto every minimal flow of the group. For some groups (for example, the locally compact ones), this flow is not metrizable and does not admit a concrete description. However, for many "large" Polish groups, the UMF is metrizable, can be computed, and carries interesting combinatorial information. The talk will concentrate on some new results that give a characterization of metrizable UMFs of Polish groups. It is based on two papers, one joint
2015 Nov 17

# Dynamics & probability: Sebastian Donoso (HUJI), "Topological structures and the pointwise convergence of some averages for commuting transformations"

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Topological structures and the pointwise convergence of some averages for commuting transformations Abstract: Topological structures'' associated to a topological dynamical system are recently developed tools in topological dynamics. They have several applications, including the characterization of topological dynamical systems, computing automorphisms groups and even the pointwise convergence of some averages.  In this talk I will discuss some developments of this subject, emphasizing applications to the pointwise convergence of some averages.