Weakly self-avoiding words and a construction of Friedman
The electronic journal of combinatorics, Tome 8 (2001) no. 1
H. Friedman obtained remarkable results about the longest finite sequence $x$ over a finite alphabet such that for all $i \ne j$ 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 self-avoiding 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.
@article{10_37236_1587,
author = {Jeffrey Shallit and Ming-wei Wang},
title = {Weakly self-avoiding words and a construction of {Friedman}},
journal = {The electronic journal of combinatorics},
year = {2001},
volume = {8},
number = {1},
doi = {10.37236/1587},
zbl = {0966.68164},
url = {http://geodesic.mathdoc.fr/articles/10.37236/1587/}
}
Jeffrey Shallit; Ming-wei Wang. Weakly self-avoiding words and a construction of Friedman. The electronic journal of combinatorics, Tome 8 (2001) no. 1. doi: 10.37236/1587
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