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

Published online by Cambridge University Press:  26 February 2010

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 = AB 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}).

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Type
Research Article
Copyright
Copyright © University College London 1993

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