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Central sets in commutative semigroups and partition regularity of systems of linear equations

Part of: Extremal combinatorics

Published online by Cambridge University Press:  26 February 2010

Neil Hindman  and
Wen-Jin Woan
Neil Hindman
Affiliation:
Department of Mathematics, Howard University, Washington, D.C. 20059, U.S.A.
Wen-Jin Woan
Affiliation:
Department of Mathematics, Howard University, Washington, D.C. 20059, U.S.A.
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Abstract

Given a commutative semigroup (S, +) with identity 0 and u × v matrices A and B with nonnegative integers as entries, we show that if C = A – B satisfies Rado's columns condition over ℤ, then any central set in S contains solutions to the system of equations . In particular, the system of equations is then partition regular. Restricting our attention to the multiplicative semigroup of positive integers (so that coefficients become exponents) we show that the columns condition over ℤ is also necessary for the existence of solutions in any central set (while the distinct notion of the columns condition over Q is necessary and sufficient for partition regularity over ℕ\{1}).

MSC classification

Secondary: 05D10: Ramsey theory
Type
Research Article
Information
Mathematika , Volume 40 , Issue 2 , December 1993 , pp. 169 - 186
Copyright
Copyright © University College London 1993

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