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On the longest common subsequence of Thue-Morse words
Information Processing Letters ( IF 0.5 ) Pub Date : 2020-08-06 , DOI: 10.1016/j.ipl.2020.106020
Joakim Blikstad

The length a(n) of the longest common subsequence of the nth Thue-Morse word and its bitwise complement is studied. An open problem suggested by Jean Berstel in 2006 is to find a formula for a(n). In this paper we prove new lower bounds on a(n) by explicitly constructing a common subsequence between the Thue-Morse words and their bitwise complement. We obtain the lower bound a(n)=2n(1o(1)), saying that when n grows large, the fraction of omitted symbols in the longest common subsequence of the nth Thue-Morse word and its bitwise complement goes to 0. We further generalize to any prefix of the Thue-Morse sequence, where we prove similar lower bounds.



中文翻译:

关于Thue-Morse单词的最长共同子序列

长度 一种ñ研究了第n个Thue-Morse单词的最长公共子序列及其按位补码。让·贝斯特尔(Jean Berstel)在2006年提出的一个开放问题是为一种ñ。在本文中,我们证明了新的下界一种ñ通过在Thue-Morse单词与其按位补语之间显式构造一个公共子序列。我们获得下界一种ñ=2ñ1个-Ø1个,说当n变大时,第n个Thue-Morse单词的最长公共子序列及其按位补码中省略符号的分数变为0。我们进一步推广到Thue-Morse序列的任何前缀,在这里我们证明相似的下限。

更新日期:2020-09-22
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