Published online by Cambridge University Press: 26 December 2018
A subset $A$ of a finite abelian group
$G$ is called
$(k,l)$-sum-free if the sum of
$k$ (not necessarily distinct) elements of
$A$ never equals the sum of
$l$ (not necessarily distinct) elements of
$A$. We find an explicit formula for the maximum size of a
$(k,l)$-sum-free subset in
$G$ for all
$k$ and
$l$ in the case when
$G$ is cyclic by proving that it suffices to consider
$(k,l)$-sum-free intervals in subgroups of
$G$. This simplifies and extends earlier results by Hamidoune and Plagne [‘A new critical pair theorem applied to sum-free sets in abelian groups’, Comment. Math. Helv. 79(1) (2004), 183–207] and Bajnok [‘On the maximum size of a
$(k,l)$-sum-free subset of an abelian group’, Int. J. Number Theory 5(6) (2009), 953–971].