
arXiv: 1510.01753
In combinatorics on words, a word $w$ over an alphabet $\Sigma$ is said to avoid a pattern $p$ over an alphabet $\Delta$ if there is no factor $f$ of $w$ such that $f=h(p)$ where $h: \Delta^*\to\Sigma^*$ is a non-erasing morphism. A pattern $p$ is said to be $k$-avoidable if there exists an infinite word over a $k$-letter alphabet that avoids $p$. A pattern is said to be doubled if no variable occurs only once. Doubled patterns with at most 3 variables and doubled patterns with at least 6 variables are $3$-avoidable. We show that doubled patterns with 4 and 5 variables are also $3$-avoidable.
FOS: Computer and information sciences, Combinatorics on words, Discrete Mathematics (cs.DM), Word, [INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM], pattern avoidance, Pattern avoidance, FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Computer Science - Discrete Mathematics
FOS: Computer and information sciences, Combinatorics on words, Discrete Mathematics (cs.DM), Word, [INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM], pattern avoidance, Pattern avoidance, FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Computer Science - Discrete Mathematics
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