IMI Interdisciplinary Mathematics InstituteCollege of Arts and Sciences

## NSF-CBMS Conference on Additive Combinatorics from a Geometric ViewpointSpeaker

Principal Lecturer
Jozsef Solymosi
University of British Columbia
http://www.math.ubc.ca/~solymosi/

Jozsef Solymosi is a Professor in the Department of Mathematics at the University of British Columbia in Vancouver. His mathematical interest includes Additive Combinatorics, Discrete and Computational Geometry, Graph theory, and Combinatorial Number Theory. He received his Master’s degree under the supervision of Laszlo Szekely from the Eotvos Lorand University in Budapest, and his PhD from the Swiss Federal Institute of Technology (ETH) Zurich under the supervision of Emo Welzl.

He was the S. E. Warschawski Assistant Professor at the Department of Mathematics, University of California, San Diego, before moving to Vancouver. Solymosi held various visiting positions; he was Member of the School of Mathematics, Institute for Advanced Study in Princeton, he was Visiting Professor at the Ecole Polytechnique Fédérale de Lausanne, and Visiting Fellow of the Isaac Newton Institute for Mathematical Sciences in Cambridge. Solymosi is a Sloan Research Fellow and has received the André Aisenstadt Mathematics Prize from the Centre de Recherches Mathématiques (CRM). He received the title Doctor of the Mathematical Sciences from the Hungarian Academy of Sciences.

Talks

## Additive structures in subsets of integers

• May 21, 2018
• 9 a.m.
• LeConte 412

Hilbert cubes, Schur's theorem and other coloring questions. When can we expect density version of a coloring problem? Density of integer sequences. In additive combinatorics one of the basic questions what can we say about the structure of sets with small sumsets. A special case is when we are considering a partitioning of the first n integers into a few partition classes. (Or, colouring the integers, which is an equivalent formulation of the problem.) The oldest result is due to Hilbert, who proved that any coloring of the integers contains a "Hilbert-cube". Schur's theorem points to stronger statements, however there the statements only hold for the coloring (partitioning) problems, no density variants hold.

## The geometry of Cartesian products

• May 21, 2018
• 2 p.m.
• LeConte 412

Szemeredi-Trotter type incidence bounds for Cartesian products. Complex lines. Grid-like Cartesian products are easier to work with than with general pointsets. They offer to state and prove toy versions of harder to prove general theorems. Still, in several applications the Cartesian product structure appears naturally, so the results can be used in additive combinatorics directly.

## Sets with small doubling numbers

• May 22, 2018
• 9 a.m.
• LeConte 412

Sum of convex sets. Distinct consecutive differences imply large sumset. The sum-product problem. Continuation of the previous lecture for a better understanding of the additive structure of sets with small sumsets. We say a few words about the incompatibility of additive and multiplicative structures.

## Introduction to Freiman's theorem

• May 22, 2018
• 10:30 a.m.
• LeConte 412

Freiman's dimension lemma and its consequences. A tool: Schmidt's Subspace Theorem. When a set has very small doubling then it has a structure similar to a (generalized) arithmetic progression. We are going to use some heavy tools from algebraic geometry to prove some interesting results.

## Problem Solving Session

• May 22, 2018
• 3 p.m.
• LeConte 412

Problem solving session led by Jozsef Solymosi.

## Quasirandomness

• May 23, 2018
• 9 a.m.
• LeConte 412

Spectral methods in graphs. When can we use the spectra? Large sets in finite fields. Quasirandomness is an important tool in additive combinatorics. We introduce the notation of quasirandomness to Cayley graphs. Then we use some basic Cheeger-type inequalities to prove results on large subsets of finite fields.

## Dense graphs. Regularity and regularity lemmas for graphs and hypergraphs

• May 23, 2018
• 11:30 a.m.
• LeConte 412

When one uses dense graphs for modelling problems in additive combinatorics, then one of the most powerful tools is Szemeredi's Regularity Lemma. An even more powerful recent result is the Removal Lemma for hypergraphs. In this lecture we introduce the basic definitions and state various forms of the theorems.

## Applications of regularity

• May 24, 2018
• 9 a.m.
• LeConte 412

The corner theorem in integer grids. The earliest application of concept of regularity appeared in Szemeredi's proof on arithmetic progressions in dense subsets of integers. Then it became a frequently used technique in graph theory and theoretical computer science. We give a simple proof based on a variant of the hypergraph removal lemma. We will also talk about the Density Hales-Jewett theorem.

## Lines in space

• May 24, 2018
• 2 p.m.
• LeConte 412

A problem of Bourgain: bounds on joints. The polynomial method. Szekely's method on hard Erdos type problems. We are giving incidence bounds between points and lines in the plane and in space. We show some classical applications of the incidence bounds.

## Problem Solving Session

• May 24, 2018
• 3:30 p.m.
• LeConte 412

Problem solving session led by Jozsef Solymosi.

## The sum-product problem over fields of characteristic zero

• May 25, 2018
• 9 a.m.
• LeConte 412

An old conjecture of Erdos and Szemeredi states that for any finite set of integers has large sumset or large product set (almost quadratic in the size of the set). We are going to prove lower bounds on the sum of the cardinalities of the sumset and the product set showing that additive and multiplicative structures are very incompatible.

## The polynomial method over finite fields

• May 25, 2018
• 1 p.m.
• LeConte 412

The sum-product problem over finite fields. The Guth-Katz polynomial method is robust enough to extend it over finite fields. Then one can use it to derive incidence bounds there, which provide bounds on the sum-product problem over finite fields. There are important applications of the sumproduct phenomena in computer science.

## Closing Discussion

• May 25, 2018
• 2:30 p.m.
• LeConte 412

Closing discussion led by Jozsef Solymosi.

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