Existence of an infinite ternary 64-abelian square-free word

Author: Huova Mari  

Publisher: Edp Sciences

E-ISSN: 1290-385x|48|3|307-314

ISSN: 0988-3754

Source: RAIRO - Theoretical Informatics and Applications, Vol.48, Iss.3, 2014-07, pp. : 307-314

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Abstract

We consider a recently defined notion of k-abelian equivalence of words by concentrating on avoidance problems. The equivalence class of a word depends on the numbers of occurrences of different factors of length k for a fixed natural number k and the prefix of the word. We have shown earlier that over a ternary alphabet k-abelian squares cannot be avoided in pure morphic words for any natural number k. Nevertheless, computational experiments support the conjecture that even 3-abelian squares can be avoided over ternary alphabets. In this paper we establish the first avoidance result showing that by choosing k to be large enough we have an infinite k-abelian square-free word over three letter alphabet. In addition, this word can be obtained as a morphic image of a pure morphic word.