Unavoidable Sets of Constant Length

نویسندگان

Jean-Marc Champarnaud

Georges Hansel

Dominique Perrin

چکیده

A set of words X is called unavoidable on a given alphabet A if every infinite word on A has a factor in X. For k, q ≥ 1, let c(k, q) be the number of conjugacy classes of words of length k on q letters. An unavoidable set of words of length k on q symbols has at least c(k, q) elements. We show that for any k, q ≥ 1 there exists an unavoidable set of words of length k on q symbols having c(k, q) elements.

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