Intervals of permutation class growth rates

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Bevan, David (2018) Intervals of permutation class growth rates. Combinatorica, 38 (2). pp. 279-303. ISSN 1439-6912 (https://doi.org/10.1007/s00493-016-3349-2)

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Abstract

We prove that the set of growth rates of permutation classes includes an infinite sequence of intervals whose infimum is θB ≈ 2.35526, and that it also contains every value at least λB ≈ 2.35698. These results improve on a theorem of Vatter, who determined that there are permutation classes of every growth rate at least λA ≈ 2.48187. Thus, we also refute his conjecture that the set of growth rates below λA is nowhere dense. Our proof is based upon an analysis of expansions of real numbers in non-integer bases, the study of which was initiated by Rényi in the 1950s. In particular, we prove two generalisations of a result of Pedicini concerning expansions in which the digits are drawn from sets of allowed values.

ORCID iDs

Bevan, David ORCID logoORCID: https://orcid.org/0000-0001-7179-2285;
CORE (COnnecting REpositories)