2019 Dec 31

# Mike Hochman (HUJI) Equidistribution for toral endomorphisms

2:00pm to 3:00pm

## Location:

Ross 70

Abstract: Host proved a strengthening of Rudolph and Johnson's measure rigidity theorem: if a probability measure is invariant, ergodic and has positive entropy for the map x2 mod 1, then a.e. point equidisitrbutes under x3 mod 1. Host also proved a version for toral endomorphisms, but its hypotheses are in some ways too strong, e.g. it requires one of the maps to be expanding, so it does not apply to pairs of  automorphisms. In this talk I will present an extension of Host's result (almost) to its natural generality.
2020 Mar 23

# Combinatorics:

Repeats every week every Monday until Mon Jun 29 2020 except Mon Apr 06 2020.
11:00am to 1:00pm

11:00am to 1:00pm
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Manchester 110

Speaker: TBA

Title: TBA

Abstract: TBA
2020 Jan 27

# Combinatorics: Chaya Keller (Ariel)

10:00am to 12:00pm

## Location:

C-400, CS building

Title: The epsilon-t-net problem

Abstract:

In this talk we study a natural generalization of the classical \eps-net problem (Haussler-Welzl 1987), which we call 'the \eps-t-net problem': Given a hypergraph on n vertices and parameters t and \eps , find a minimum-sized family S of t-element subsets of vertices such that each hyperedge of size at least \eps n  contains a set in S. When t=1, this corresponds to the \eps-net problem.
2020 Jan 13

# Combinatorics: Michael Simkin (HUJI)

10:00am to 12:00pm

## Location:

C-400, CS building

Title: A randomized construction of high girth regular graphs

Abstract: We describe a new random greedy algorithm for generating regular graphs of high girth: Let $k > 2$ and $0 < c < 1$ be fixed. Let $n$ be even and set $g = c \log_{k-1} (n)$. Begin with a Hamilton cycle $G$ on $n$ vertices. As long as the smallest degree $\delta (G)<k$, choose, uniformly at random, two vertices $u,v \in V(G)$ of degree $\delta(G)$ whose distance is at least $g-1$. If there are no such vertex pairs, abort. Otherwise, add the edge $uv$ to $E(G)$.
2019 Dec 30

# Combinatorics: Gal Kronenberg (Oxford)

10:00am to 12:00pm

## Location:

C-400, CS building

Speaker: Gal Kronenberg (Oxford)

Title: The chromatic index of random multigraphs

Abstract:
2020 Apr 27

# Combinatorics: Noam Lifshitz (HUJI)

11:00am to 1:00pm

## Location:

Zoom

Speaker: Noam Lifshitz (HUJI)

Title: Forbidden intersections for permutations
2020 Jan 20

# Combinatorics: Wojciech Samotij (TAU)

10:00am to 12:00pm

## Location:

C-400, CS building

Title: The lower tail for triangles in random graphs

Abstract:
2020 Jan 06

# Combinatorics: Sarah Peluse (Oxford)

10:00am to 12:00pm

## Location:

C-400, CS building

Speaker: Sarah Peluse (Oxford)

Title: Bounds in the polynomial Szemer\'edi theorem
2019 Dec 23

# Combinatorics: Yinon Spinka (UBC)

10:00am to 12:00pm

## Location:

C-400, CS building

Speaker: Yinon Spinka (UBC)

Title: Random graphs on the circle

Abstract: It has long been known that two independent copies of the infinite Erdos-Renyi graph G(\infty,p) are almost surely isomorphic. The resulting graph is called the Rado graph. If the vertices are in a metric space and only nearby vertices may be connected, a similar result may or may not hold, depending on fine details of the underlying metric space. We present new results in the case where the metric space is a circle.
2020 Jan 09

# Basic Notions: Menachem Magidor (HUJI) "Regularity properties of subsets of the real line and other polish spaces"

4:00pm to 5:15pm

## Location:

Ross 70
Using the axiom of choice one can construct set of reals which are
pathological in some sense. Similar constructions can be produce such
"pathological" subsets of any non trivial Polish space (= a complete
separable metric space).
A "pathological set" can be a non measurable set , a set which does
not have the property of Baire (namely it is not a Borel set modulo a
rst category set).
A subset of the innite subsets of natural numbers,
can be considered to be "pathological" if it is a counter example to
2019 Dec 26

# Basic Notions: Menachem Magidor (HUJI) "Regularity properties of subsets of the real line and other polish spaces"

4:00pm to 5:15pm

## Location:

Ross 70
Using the axiom of choice one can construct set of reals which are
pathological in some sense. Similar constructions can be produce such
"pathological" subsets of any non trivial Polish space (= a complete
separable metric space).
A "pathological set" can be a non measurable set , a set which does
not have the property of Baire (namely it is not a Borel set modulo a
rst category set).
A subset of the innite subsets of natural numbers,
can be considered to be "pathological" if it is a counter example to
2019 Dec 11

# Logic Seminar - Eliana Bariga

11:00am to 1:00pm

## Location:

Ross building - Room 63
Eliana Bariga will speak about Definably compact semialgebraic groups over real closed fields.

Abstract:
Semialgebraic groups over a real closed field can be seen as a generalization of the semialgebraic groups over the real field, and also as a particular case of the groups definable in an o-minimal structure.
2020 Jan 16

# Lev Glebsky (UASLP): Residually finite by residually finite extensions are weakly sofic

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
January 16, 12:00-13:00, Seminar room 209, Manchester building.

Abstract: I plan to show a proof of the statement  "residually-finite-by-residually-finite extensions are weakly sofic". The proof is based on characterization of weakly sofic groups
by solvability of equations over groups. It looks different from other proofs of soficity and weak soficity. I plan to discuss relations of equations on and over groups with soficity in some details.

2019 Dec 05

# Basic Notions: Eran Nevo

4:00pm to 5:30pm

## Location:

Ross 70
Eran Nevo with continue his presentation of the Stanley-Reisner theory.
2019 Dec 03

# Logic Seminar - Antongiulio Fornasiero

1:00pm to 3:00pm

## Location:

Shprintsak building - Room 29
OAntongiulio Fornasiero will speak about definable and interpretable groups and fields in the p-adics.

Abstract:
A. Pillay showed that every definable group in the p-adics has a canonical topology and differential structure, and deduced that every definable field is either finite or a finite extension of Q_p.
In a joint work with J. de la Nuez Gonzalez we extend the analysis to interpretable fields, and show that they are either countable or finite extensions of Q_p.