On minimal critical exponent of balanced sequences
| Autor: | L'ubomíra Dvořáková, Edita Pelantová, Daniela Opočenská, Arseny M. Shur |
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| Jazyk: | angličtina |
| Rok vydání: | 2022 |
| Předmět: |
RETURN WORDS
General Computer Science BALANCED SEQUENCES 68R15 Theoretical Computer Science RETURN WORD BISPECIAL FACTOR CONSTANT GAP SEQUENCE CRITICAL EXPONENT FOS: Mathematics Mathematics - Combinatorics STURMIAN SEQUENCES Combinatorics (math.CO) STURMIAN SEQUENCE BALANCED SEQUENCE REPETITION THRESHOLD FINITE ALPHABET |
| Zdroj: | Theoretical Computer Science |
| Popis: | We study the threshold between avoidable and unavoidable repetitions in infinite balanced sequences over finite alphabets. The conjecture stated by Rampersad, Shallit and Vandomme says that the minimal critical exponent of balanced sequences over the alphabet of size $d \geq 5$ equals $\frac{d-2}{d-3}$. This conjecture is known to hold for $d\in \{5, 6, 7,8,9,10\}$. We refute this conjecture by showing that the picture is different for bigger alphabets. We prove that critical exponents of balanced sequences over an alphabet of size $d\geq 11$ are lower bounded by $\frac{d-1}{d-2}$ and this bound is attained for all even numbers $d\geq 12$. According to this result, we conjecture that the least critical exponent of a balanced sequence over $d$ letters is $\frac{d-1}{d-2}$ for all $d\geq 11$. Comment: 20 pages; 2 figures |
| Databáze: | OpenAIRE |
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