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arXiv 0909.2461math.COmath.NT
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关于循环群上序列的指数

On the Index of Sequences over Cyclic Groups

Weidong Gao, Yuanlin Li, Jiangtao Peng, Chris Plyley, Guoqing Wang

摘要:

设$G$是$n \ge 2$阶的有限循环群.每个序列$S$ over $G$可以写成$S=(n_1g)\cdot ... \cdot (n_lg)$的形式,其中$g\in G$和$n_1,..., n_l \in [1,\ord(g)]$,并且$S$的索引$\ind (S)$被定义为所有具有$\ord (g) = n$的$g \in G$上的$(n_1+ ... + n_l)/\ord (g)$的最小值。本文证明了一个序列$S$在$G$上的长度为$|S| = n$且其重数至少为$\frac{n}{2}$的序列有一个子序列$T$,其重数至少为$\ind (T) = 1$,并且如果群序$n$是素数,则重数的假设可以放宽为$\frac{n-2}{10}$ .另一方面,如果$n=4k+2$具有$k \ge 5$,我们提供了一个序列$S$的例子,该序列具有长度$|S| > n$和具有多重性$\frac{n}{2}-1$的元素,该元素没有具有$\ind (T) = 1$的子序列$T$。这就推翻了莱姆克和克莱特曼20年前提出的一个猜想。

英文摘要:

Let $G$ be a finite cyclic group of order $n \ge 2$. Every sequence $S$ over $G$ can be written in the form $S=(n_1g)\cdot ... \cdot (n_lg)$ where $g\in G$ and $n_1,..., n_l \in [1,\ord(g)]$, and the index $\ind (S)$ of $S$ is defined as the minimum of $(n_1+ ... + n_l)/\ord (g)$ over all $g \in G$ with $\ord (g) = n$. In this paper we prove that a sequence $S$ over $G$ of length $|S| = n$ having an element with multiplicity at least $\frac{n}{2}$ has a subsequence $T$ with $\ind (T) = 1$, and if the group order $n$ is a prime, then the assumption on the multiplicity can be relaxed to $\frac{n-2}{10}$. On the other hand, if $n=4k+2$ with $k \ge 5$, we provide an example of a sequence $S$ having length $|S| > n$ and an element with multiplicity $\frac{n}{2}-1$ which has no subsequence $T$ with $\ind (T) = 1$. This disproves a conjecture given twenty years ago by Lemke and Kleitman.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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