2016 Dec 19

# Combinatorics: Lukas Kühne (U. Bonn) "Heavy hyperplanes in multiarrangements and their freeness"

11:00am to 1:00pm

## Location:

Rothberg B220 (CS)
Speaker: Lukas Kühne (University of Bonn) Title: Heavy hyperplanes in multiarrangements and their freeness Abstract: One of the central topics among the theory of hyperplane arrangements is their freeness. Terao's conjecture tries to link the freeness with the combinatorics of an arrangement. One of the few categories of arrangements which satisfy this conjecture consists of 3-dimensional arrangements with an unbalanced Ziegler restriction. This means that the arrangement contains a lot of hyperplanes intersecting in one single line
2017 Nov 20

# Combinatorics seminar:Sria Louis

11:00am to 12:30pm

## Location:

IIAS Room 130
Speaker 1: Sria Louis Title: Asymptotically Almost Every 2r-regular Graph has an Internal Partition Abstract: An internal partition of a graph is a partitioning of the vertex set into two parts such that for every vertex, at least half of its neighbors are on its side. It is easy to notice that such a partition doesn't always exist (e.g. - cliques), though, both the existence and finding of such a partition - are open problems. Stiebitz (1996), responding to a problem of Thomassen (1983), made a breakthrough in this area, but the question and some interesting generalizations are still open.
2017 Mar 06

# Combinatorics: Zilin Jiang (Technion) "Relations between Tverberg points and central points"

11:00am to 1:00pm

## Location:

Rothberg B220 (CS)
Speaker: Zilin Jiang (Technion) Title: Relations between Tverberg points and central points Abstract: Given 3n lines in general position in the plane, it is always possible to partition them into n triples of lines so that all the triangles, formed by the triples, share a common point. This result is known back in 1988 by J.P. Roudneff. Strangely, in higher dimensions, it is only proved by Roman Karasev for n that is a prime power.
2016 Feb 29

# Combinatorics

Repeats every week every Monday until Mon Jun 13 2016 .
10:30am to 12:30pm

10:30am to 12:30pm
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## Location:

B220 Rothberg (CS and Engineering building)
NOTE THE SPECIAL TIME: 11:00--12:30 Speaker: Eyal Ackerman, University of Haifa at Oranim Title: Coloring points with respect to squares Abstract: Is there an absolute constant $m$ such that any finite planar point set can be 2-colored such that every axis-parallel square that contains at least $m$ points contains points of both colors? I will discuss this problem and related ones.
2018 Mar 26

# Combinatorics seminar: Chaim Even Zohar, UC Davis, TBA

10:30am to 12:30pm

2016 Dec 05

# Combinatorics: Klim Efremenko (TAU) " Testing Equality in Communication Graphs"

11:00am to 1:00pm

## Location:

B220 Rothberg (CS)
Speaker: Klim Efremenko (TAU) Title: Testing Equality in Communication Graphs Abstract: Let G=(V,E) be a connected undirected graph with k vertices. Suppose that on each vertex of the graph there is a player having an n-bit string. Each player is allowed to communicate with its neighbors according to a (static) agreed communication protocol and the players must decide, deterministically, if their inputs are all equal. What is the minimum possible total number of bits transmitted in a protocol solving this problem? We determine this minimum up to a lower order
2017 May 04

# Amitsur Algebra: Jasbir Chahal, " A tale of three elliptic curves"

12:00pm to 1:00pm

## Location:

Manchester 209
Title: A tale of three elliptic curves. Abstract: We will show how the arithmetic of three elliptic curves answers three old questions in the Euclidean geometry.
2016 Dec 08

# Amitsur Algebra: George Glauberman (Chicago)

12:00pm to 1:15pm

## Location:

Manchester Building, Room 209
Title: Fixed points of finite groups on modules Abstract: Suppose G is a finite group, p is a prime, S is a Sylow p-subgroup of G, and V is a G-module over a field of characteristic p. In some situations, an easy calculation shows that the fixed points of G on V are the same as the fixed points of the normalizer of S in G. Generalizations of this result have been obtained previously to study the structure of G for p odd. We plan to describe a new generalization for p = 2. (This is part of joint work with J. Lynd that removes the classification of finite simple groups
2017 Mar 02

# Amitsur Algebra: Lev Glebsky, " Almost Congruence Extension Property for subgroups of free groups"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Almost Congruence Extension Property for subgroups of free groups. Abstract. The talk essentially based on: https://arxiv.org/abs/1606.02345 Let G be a group and H
2017 Feb 09

# Amitsur Algebra: Evan DeCorte, "The spectral method for geometric colouring problems"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: The spectral method for geometric colouring problems
2017 Jun 29

12:00pm to 1:00pm

## Location:

Manchester 209
Title: Stability patterns in representation theory and applications Abstract: Many natural sequences of objects come equipped with group actions, e.g. the symmetric group on n letters acting on a space X_n. This leads to fundamental instability of invariants, such as homology, arising from the representation theory of the sequence of groups. Representation stability is a new and increasingly important set of ideas that describe a sense in which such sequence of representations (of different groups) stabilizes.
2017 Jan 12

# Amitsur Algebra: Uriya First, "Semisimply degenerate quadratic forms and a conjecture of Grothendieck and Serre"

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: Semisimply degenerate quadratic forms and a conjecture of Grothendieck and Serre (joint work with E. Bayer-Fluckiger) Abstract:
2017 May 25

# Amitsur Algebra: Katrin Tent, "Sharply 2- and 3-transitive groups"

12:00pm to 1:00pm

## Location:

Manchester 209
The existence of sharply 2-transitive groups without regular normal subgroup was a longstanding open problem. Recently constructions have been given, at least in certain characteristics. We will survey the current state of the art and explain some constructions and their limitations. (joint work with E. Rips)
2016 Dec 22

# Amitsur Algebra: Mark Sapir (Vanderbilt)

12:00pm to 1:00pm

## Location:

Manchester Building, Room 209
Title: On groups with quadratic Dehn functions Abstract: This is a joint work with A. Olshanskii. We construct a finitely presented group with quadratic Dehn function and undecidable conjugacy problem.
2017 Mar 23

# Amitsur Algebra: Daniel Palacin, "Pseudo-finite groups containing an involution with a finite centralizer"

12:00pm to 1:00pm

## Location:

Manchester 209
Title: Pseudo-finite groups containing an involution with a finite centralizer.