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arXiv · 2105.08242

Equivalence of the Descents Statistic on Some (4,4)-Avoidance Classes of Permutations

Toufik Mansour·Mark Shattuck
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Abstract

In this paper, we compute and demonstrate the equivalence of the joint distribution of the first letter and descent statistics on six avoidance classes of permutations corresponding to two patterns of length four. This distribution is in turn shown to be equivalent to the distribution on a restricted class of inversion sequences for the statistics that record the last letter and number of distinct positive letters, affirming a recent conjecture of Lin and Kim. Members of each avoidance class of permutations and also of the class of inversion sequences are enumerated by the $n$-th large Schr\"oder number and thus one obtains a new bivariate refinement of these numbers as a consequence. We make use of auxiliary combinatorial statistics, special generating functions (specific to each class) and the kernel method to establish our results. In some cases, we utilize the conjecture itself in a creative way to aid in solving the system of functional equations satisfied by the associated generating functions.

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Toufik Mansour, Mark Shattuck. 2021-05-18. Equivalence of the Descents Statistic on Some (4,4)-Avoidance Classes of Permutations. https://arxiv.org/abs/2105.08242

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