English

Fewest repetitions in infinite binary words

Discrete Mathematics 2012-07-25 v1

Abstract

A square is the concatenation of a nonempty word with itself. A word has period p if its letters at distance p match. The exponent of a nonempty word is the quotient of its length over its smallest period. In this article we give a proof of the fact that there exists an infinite binary word which contains finitely many squares and simultaneously avoids words of exponent larger than 7/3. Our infinite word contains 12 squares, which is the smallest possible number of squares to get the property, and 2 factors of exponent 7/3. These are the only factors of exponent larger than 2. The value 7/3 introduces what we call the finite-repetition threshold of the binary alphabet. We conjecture it is 7/4 for the ternary alphabet, like its repetitive threshold.

Cite

@article{arxiv.1207.5723,
  title  = {Fewest repetitions in infinite binary words},
  author = {Golnaz Badkobeh and Maxime Crochemore},
  journal= {arXiv preprint arXiv:1207.5723},
  year   = {2012}
}
R2 v1 2026-06-21T21:40:43.363Z