Special factors of automatic sequences. (English) Zbl 0856.11012

The author defines a special factor \(v\) of an infinite sequence \(u\) on a finite alphabet \(A\) to be a finite factor (subblock) of \(u\) such that, for each letter \(a\in A\), the word \(va\) is also a factor of \(u\). Such words are sometimes called extendable, but note that a more general definition only assumes that \(va\) is a factor for at least one letter \(a\) [see for example: J. Cassaigne, Complexité et facteurs spéciaux, Bull. Belg. Math. Soc. (to appear)].
In order to study the special factors of infinite fixed points of morphisms, the author introduces the notion of rythmical word (essentially a word that is the “unique” image of another word by the morphism). Note that a recent paper by B. Mossé [Reconnaissabilité des substitutions et complexité des suites automatiques, Bull. Soc. Math. Fr. 124, 329-346 (1996; Zbl 0855.68072)] gives complementary results.


11B85 Automata sequences
68R15 Combinatorics on words


Zbl 0855.68072
Full Text: DOI


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