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Monochromatic arithmetic progressions in automatic sequences with group structure
Journal of Combinatorial Theory Series A ( IF 1.1 ) Pub Date : 2023-12-01 , DOI: 10.1016/j.jcta.2023.105831
Ibai Aedo , Uwe Grimm , Neil Mañibo , Yasushi Nagai , Petra Staynova

We determine asymptotic growth rates for lengths of monochromatic arithmetic progressions in certain automatic sequences. In particular, we look at (one-sided) fixed points of aperiodic, primitive, bijective substitutions and spin substitutions, which are generalisations of the Thue–Morse and Rudin–Shapiro substitutions, respectively. For such infinite words, we show that there exists a subsequence {dn} of differences along which the maximum length A(dn) of a monochromatic arithmetic progression (with fixed difference dn) grows at least polynomially in dn. Explicit upper and lower bounds for the growth exponent can be derived from a finite group associated to the substitution. As an application, we obtain bounds for a van der Waerden-type number for a class of colourings parametrised by the size of the alphabet and the length of the substitution.



中文翻译:

具有群结构的自动序列中的单色算术级数

我们确定某些自动序列中单色算术级数长度的渐近增长率。特别是,我们研究非周期、本原、双射替换和自旋替换的(单边)不动点,它们分别是 Thue-Morse 和 Rudin-Shapiro 替换的推广。对于这样的无限单词,我们证明存在一个子序列{dn}最大长度的差异Adn单色算术级数(具有固定差值)dn) 至少以多项式增长dn。增长指数的显式上限和下限可以从与替换相关的有限群中导出。作为一个应用,我们获得一类着色的 van der Waerden 型数字的界限,该颜色由字母表的大小和替换的长度参数化。

更新日期:2023-12-01
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