Quasi-Randomness in Extremal Combinatorics

Project Information

EXTPRO

Grant agreement ID: 633509

DOI

10.3030/633509

Project closed

EC signature date 16 February 2015

Start date 1 March 2015

End date 28 February 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 221 921,00

EU contribution

€ 1 221 921,00

Coordinated by

TEL AVIV UNIVERSITY
Israel

Periodic Reporting for period 4 - EXTPRO (Quasi-Randomness in Extremal Combinatorics)

Reporting period: 2019-09-01 to 2021-02-28

Summary of the context and overall objectives of the project

In object is quasi-random if it behaves (in certain well defines ways) like we would expect a typical object to behave. The goal of this project is to better understand the role and the applicability of various notions of quasi-randomness in discrete mathematics, that is, in the study of discrete objects such as networks, strings of characters. The surprising fact, is that we can study arbitrary object, that is, even those that do NOT behave like typical one, using tools developed to handle objects that do behave this way. For example, we might try to show that every string can be broken into few strings, each of which is quasi-random. This can allow us to prove theorems or design algorithms by making the assumption that the input has some nice properties (even though it doesn’t), thus making these tasks much easier.
Within the above framework, I mainly try to prove theorems on graph and hypergraphs specifically regarding the connections between local and global properties of such objects. I also try to use these insights in order to design very fast algorithms for solving various problem on such objects.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main results we have obtained are the following:
1. We obtained a tight bound for Green’s arithmetic regularity lemma.
2. We proved a tight bound for the hypergraph regularity lemma.
3. We laid out a new graph theoretic approach for solving a famous conjecture regarding the density of matrices avoiding certain patters.
4. We obtained a new proof of Fox’s famous bound for the graph removal lemma.
5. We obtained a new general sufficient for polynomially bounded removal lemmas. In particular, we proved that every semi-algebraic graph property has an efficient removal lemma.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

1. Obtain polynomial bounds for the induced C_4 removal lemma
2. Find a characterization of the linear equations for which one can prove a polynomial bounds for their removal lemma.
3. Prove supersaturation results over product posets.