Weakly Self-Avoiding Words and a Construction of Friedman
نویسندگان
چکیده
H. Friedman obtained remarkable results about the longest finite sequence x over a finite alphabet such that for all i 6= j the word x[i..2i] is not a subsequence of x[j..2j]. In this note we consider what happens when “subsequence” is replaced by “subword”; we call such a sequence a “weakly selfavoiding word”. We prove that over an alphabet of size 1 or 2, there is an upper bound on the length of weakly self-avoiding words, while if the alphabet is of size 3 or more, there exists an infinite weakly self-avoiding word.
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عنوان ژورنال:
- Electr. J. Comb.
دوره 8 شماره
صفحات -
تاریخ انتشار 2001