Separating strings with small automata
Information Processing Letters
Algorithmic number theory
On a reconstruction problem for sequences
Journal of Combinatorial Theory Series A
Separating words with small grammars
Journal of Automata, Languages and Combinatorics
DCFS'11 Proceedings of the 13th international conference on Descriptional complexity of formal systems
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Separating words with automata is a longstanding open problem in combinatorics on words. In this paper we present a related algebraic problem. What is the minimal length of a nontrivial identical relation in the symmetric group Sn? Our main contribution is an upper bound $2^{O(\sqrt n\log n)}$ on the length of the shortest nontrivial identical relation in Sn. We also give lower bounds for words of a special types. These bounds can be applied to the problem of separating words by reversible automata. In this way we obtain an another proof of the Robson’s square root bound.