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A branch of combinatorics that focuses on the study of words and formal languages

8 votes

Three-halves-free words (analogous to square-free)

This is not an answer, but it may help. According to A generalization of repetition threshold by Lucian Iliea, Pascal Ochemb, and Jeffrey Shallit (Theoretical Computer Science, Volume 345, Issues 2–3 …
JRN's user avatar
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4 votes
4 answers
724 views

Subwords of cube-free binary words

I'm currently working on subwords of cube-free binary words. A binary word is one composed of letters from a two-letter alphabet such as $\{0,1\}$. A word $y$ is a subword of $w$ if there exist word …
JRN's user avatar
  • 1,329
20 votes
4 answers
3k views

Cube-free infinite binary words

A word $y$ is a subword of $w$ if there exist words $x$ and $z$ (possibly empty) such that $w=xyz$. Thus, $01$ is a subword of $0110$, but $00$ is not a subword of $0110$. I'm interested in right-in …
JRN's user avatar
  • 1,329
7 votes

Is it possible to create an infinite sequence in which no subsequence is repeated 3 times in...

For the question in the title, you're looking for cube-free infinite words. Of special interest are cube-free infinite words that are binary (use an alphabet of two letters). A lot of work has been …
JRN's user avatar
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4 votes

Concatenation of strings

Your question seems to be answered by Theorem 1.5.3 of Allouche and Shallit's Automatic Sequences: Theory, Applications, Generalizations (Cambridge University Press, 2003). Let $x,y\in\Sigma^+$. …
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