On ternary square-free circular words
The electronic journal of combinatorics, Tome 17 (2010)
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Circular words are cyclically ordered finite sequences of letters. We give a computer-free proof of the following result by Currie: square-free circular words over the ternary alphabet exist for all lengths $l$ except for 5, 7, 9, 10, 14, and 17. Our proof reveals an interesting connection between ternary square-free circular words and closed walks in the $K_{3{,}3}$ graph. In addition, our proof implies an exponential lower bound on the number of such circular words of length $l$ and allows one to list all lengths $l$ for which such a circular word is unique up to isomorphism.
Arseny M. Shur. On ternary square-free circular words. The electronic journal of combinatorics, Tome 17 (2010). doi: 10.37236/412
@article{10_37236_412,
author = {Arseny M. Shur},
title = {On ternary square-free circular words},
journal = {The electronic journal of combinatorics},
year = {2010},
volume = {17},
doi = {10.37236/412},
zbl = {1213.68480},
url = {http://geodesic.mathdoc.fr/articles/10.37236/412/}
}
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