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arXiv · 2403.05113

On the set partitions that require maximum sorts through the $aba-$avoiding stack

Yunseo Choi·Katelyn Gan·Andrew Li·Tiffany Zhu
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Abstract

Recently, Xia introduced a deterministic variation $\phi_{\sigma}$ of Defant and Kravitz's stack-sorting maps for set partitions and showed that any set partition $p$ is sorted by $\phi^{N(p)}_{aba}$, where $N(p)$ is the number of distinct alphabets in $p$. Xia then asked which set partitions $p$ are not sorted by $\phi_{aba}^{N(p)-1}$. In this note, we prove that the minimal length of a set partition $p$ that is not sorted by $\phi_{aba}^{N(p)-1}$ is $2N(p)$. Then we show that there is only one set partition of length $2N(p)$ and ${{N(p) + 1} \choose 2} + 2{N(p) \choose 2}$ set partitions of length $2N(p)+1$ that are not sorted by $\phi_{aba}^{N(p)-1}$.

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Yunseo Choi, Katelyn Gan, Andrew Li, Tiffany Zhu. 2024-03-08. On the set partitions that require maximum sorts through the $aba-$avoiding stack. https://arxiv.org/abs/2403.05113

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