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The critical exponent of an infinite word $\bf x$ is the supremum, over all finite nonempty factors $f$, of the exponent of $f$. In this note we show that for all integers $k\geq 2,$ there is a binary infinite $k$-automatic sequence with…

Combinatorics · Mathematics 2026-02-25 J. -P. Allouche , N. Rampersad , J. Shallit

We find the lexicographically least infinite binary rich word having critical exponent $2+\sqrt{2}/2$

Formal Languages and Automata Theory · Computer Science 2023-10-12 James Currie , Narad Rampersad

The (bitwise) complement $\overline{x}$ of a binary word $x$ is obtained by changing each $0$ in $x$ to $1$ and vice versa. An $\textit{antisquare}$ is a nonempty word of the form $x\, \overline{x}$. In this paper, we study infinite binary…

Combinatorics · Mathematics 2024-02-14 Aseem Baranwal , James Currie , Lucas Mol , Pascal Ochem , Narad Rampersad , Jeffrey Shallit

We characterize the squares occurring in infinite overlap-free binary words and construct various alpha power-free binary words containing infinitely many overlaps.

Combinatorics · Mathematics 2007-05-23 James Currie , Narad Rampersad , Jeffrey Shallit

Over an alphabet of size 3 we construct an infinite balanced word with critical exponent 2+sqrt(2)/2. Over an alphabet of size 4 we construct an infinite balanced word with critical exponent (5+sqrt(5))/4. Over larger alphabets, we give…

Combinatorics · Mathematics 2018-01-17 Narad Rampersad , Jeffrey Shallit , Élise Vandomme

We study infinite binary words that contain few distinct palindromes. In particular, we classify such words according to their critical exponents. This extends results by Fici and Zamboni [TCS 2013]. Interestingly, the words with 18 and 20…

Combinatorics · Mathematics 2024-03-27 L'ubomíra Dvořáková , Pascal Ochem , Daniela Opočenská

An overlap-free (or $\beta$-free) word $w$ over a fixed alphabet $\Sigma$ is extremal if every word obtained from $w$ by inserting a single letter from $\Sigma$ at any position contains an overlap (or a factor of exponent at least $\beta$,…

Combinatorics · Mathematics 2020-06-19 Lucas Mol , Narad Rampersad , Jeffrey Shallit

The complement $\overline{x}$ of a binary word $x$ is obtained by changing each $0$ in $x$ to $1$ and vice versa. We study infinite binary words $\bf w$ that avoid sufficiently large complementary factors; that is, if $x$ is a factor of…

The abelian critical exponent of an infinite word $w$ is defined as the maximum ratio between the exponent and the period of an abelian power occurring in $w$. It was shown by Fici et al. that the set of finite abelian critical exponents of…

Formal Languages and Automata Theory · Computer Science 2019-09-17 Jarkko Peltomäki , Markus A. Whiteland

The critical exponent of an infinite word is defined to be the supremum of the exponent of each of its factors. For k-automatic sequences, we show that this critical exponent is always either a rational number or infinite, and its value is…

Formal Languages and Automata Theory · Computer Science 2011-12-13 Luke Schaeffer , Jeffrey Shallit

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…

Discrete Mathematics · Computer Science 2012-07-25 Golnaz Badkobeh , Maxime Crochemore

In this paper, we study the critical exponent of infinite words $\ubeta$ coding $\beta$-integers for $\beta$ being a~non-simple Parry number. In other words, we investigate the maximal consecutive repetitions of factors that occur in the…

Combinatorics · Mathematics 2017-05-31 L. Balková , K. Klouda , E. Pelantová

Richomme asked the following question: what is the infimum of the real numbers $\alpha$ > 2 such that there exists an infinite word that avoids $\alpha$-powers but contains arbitrarily large squares beginning at every position? We resolve…

Combinatorics · Mathematics 2009-04-14 James D. Currie , Narad Rampersad

We study infinite ternary words that contain few distinct palindromes. In particular, we classify such words according to their critical exponent.

Combinatorics · Mathematics 2026-04-01 Ľubomíra Dvořáková , Lucas Mol , Pascal Ochem

We study how much injective morphisms can increase the repetitiveness of a given word. This question has a few possible variations depending on the meaning of ``repetitiveness''. We concentrate on fractional exponents of finite words and…

Combinatorics · Mathematics 2025-06-06 Eva Foster , Aleksi Saarela , Aleksi Vanhatalo

A word of length $n$ is rich if it contains $n$ nonempty palindromic factors. An infinite word is rich if all of its finite factors are rich. Baranwal and Shallit produced an infinite binary rich word with critical exponent $2+\sqrt{2}/2$…

Combinatorics · Mathematics 2023-06-22 James D. Currie , Lucas Mol , Narad Rampersad

Generalizing the results of Thue (for n = 2) and of Klepinin and Sukhanov (for n = 3), we prove that for all n greater than or equal to 2, the critical exponent of the Arshon word of order $n$ is given by (3n-2)/(2n-2), and this exponent is…

Combinatorics · Mathematics 2008-04-03 Dalia Krieger

An infinite word is an infinite Lyndon word if it is smaller, with respect to the lexicographic order, than all its proper suffixes, or equivalently if it has infinitely many finite Lyndon words as prefixes. A characterization of binary…

Discrete Mathematics · Computer Science 2021-05-05 Gwenaël Richomme , Patrice Séébold

Recently, the authors showed that for every irrational number $\alpha$, there exist infinitely many positive integers $n$ represented by any given positive definite binary quadratic form $Q$, satisfying $||\alpha n||<n^{-(1/2-\varepsilon)}$…

Number Theory · Mathematics 2026-02-04 Stephan Baier , Habibur Rahaman

We show that the equality language of two non-periodic binary morphisms is generated by at most two words. If its rank is two, then the generators start (and end) with different letters. This in particular implies that any binary language…

Formal Languages and Automata Theory · Computer Science 2012-09-19 Štěpán Holub
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