# Proceedings of the American Mathematical Society

Published by the American Mathematical Society since 1950, Proceedings of the American Mathematical Society is devoted to shorter research articles in all areas of pure and applied mathematics.

ISSN 1088-6826 (online) ISSN 0002-9939 (print)

The 2020 MCQ for Proceedings of the American Mathematical Society is 0.85.

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## Partition regularity without the columns propertyHTML articles powered by AMS MathViewer

by Ben Barber, Neil Hindman, Imre Leader and Dona Strauss
Proc. Amer. Math. Soc. 143 (2015), 3387-3399 Request permission

## Abstract:

A finite or infinite matrix $A$ with rational entries is called partition regular if whenever the natural numbers are finitely coloured there is a monochromatic vector $x$ with $Ax=0$. Many of the classical theorems of Ramsey Theory may naturally be interpreted as assertions that particular matrices are partition regular. In the finite case, Rado proved that a matrix is partition regular if and only it satisfies a computable condition known as the columns property. The first requirement of the columns property is that some set of columns sums to zero.

In the infinite case, much less is known. There are many examples of matrices with the columns property that are not partition regular, but until now all known examples of partition regular matrices did have the columns property. Our main aim in this paper is to show that, perhaps surprisingly, there are infinite partition regular matrices without the columns property — in fact, having no set of columns summing to zero.

We also make a conjecture that if a partition regular matrix (say with integer coefficients) has bounded row sums then it must have the columns property, and prove a first step towards this.

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• Ben Barber
• Affiliation: School of Mathematics, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
• Email: b.a.barber@bham.ac.uk
• Neil Hindman
• Affiliation: Department of Mathematics, Howard University, Washington, DC 20059
• MR Author ID: 86085
• Email: nhindman@aol.com
• Affiliation: Department of Pure Mathematics and Mathematical Statistics, Centre for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 0WB, United Kingdom
• MR Author ID: 111480