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Erd\H{o}s-Ginzburg-Ziv theorem for finite commutative semigroups

Combinatorics 2013-10-22 v2 Commutative Algebra Number Theory

Abstract

Let S\mathcal{S} be a finite commutative semigroup written additively, and let exp(S)\exp(\mathcal{S}) be its exponent which is defined as the least common multiple of all periods of the elements in S\mathcal{S}. For every sequence TT of elements in S\mathcal{S} (repetition allowed), let σ(T)S\sigma(T) \in \mathcal{S} denote the sum of all terms of TT. Define the Davenport constant D(S)D(\mathcal{S}) of S\mathcal{S} to be the least positive integer dd such that every sequence TT over S\mathcal{S} of length at least dd contains a proper subsequence TT' with σ(T)=σ(T)\sigma(T')=\sigma(T), and define the Erd\H{o}s-Ginzburg-Ziv Theorem constant E(S)E(\mathcal{S}) to be the least positive integer \ell such that every sequence TT over S\mathcal{S} of length at least \ell contains a subsequence TT' with TT=Sexp(S)exp(S)|T|-|T'|=\left\lceil\frac{|\mathcal{S}|}{\exp(\mathcal{S})}\right\rceil\exp(\mathcal{S}) and σ(T)=σ(T)\sigma(T')=\sigma(T). When S\mathcal{S} is a finite abelian group, it is well known that Sexp(S)exp(S)=S\left\lceil\frac{|\mathcal{S}|}{\exp(\mathcal{S})}\right\rceil\exp(\mathcal{S})=|\mathcal{S}| and E(S)=D(S)+S1E(\mathcal{S})=D(\mathcal{S})+|\mathcal{S}|-1. In this paper we investigate whether E(S)D(S)+Sexp(S)exp(S)1E(\mathcal{S})\leq D(\mathcal{S})+\left\lceil\frac{|\mathcal{S}|}{\exp(\mathcal{S})}\right\rceil \exp(\mathcal{S})-1 holds true for all finite commutative semigroups S\mathcal{S}. We provide a positive answer to the question above for some classes of finite commutative semigroups, including group-free semigroups, elementary semigroups, and archimedean semigroups with certain constraints.

Keywords

Cite

@article{arxiv.1309.5588,
  title  = {Erd\H{o}s-Ginzburg-Ziv theorem for finite commutative semigroups},
  author = {Sukumar Das Adhikari and Weidong Gao and Guoqing Wang},
  journal= {arXiv preprint arXiv:1309.5588},
  year   = {2013}
}

Comments

19 pages, accepted by Semigroup Forum