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arXiv · 2502.13309

Pattern avoidance in non-crossing and non-nesting permutations

Kassie Archer·Robert P. Laudone
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Abstract

Non-crossing and non-nesting permutations are variations of the well-known Stirling permutations. A permutation $π$ on $\{1,1,2,2,\ldots, n,n\}$ is called non-crossing if it avoids the crossing patterns $\{1212,2121\}$ and is called non-nesting if it avoids the nesting patterns $\{1221,2112\}.$ Pattern avoidance in these permutations has been considered in recent years, but it has remained open to enumerate the non-crossing and non-nesting permutations that avoid a single pattern of length 3. In this paper, we provide generating functions for those non-crossing and non-nesting permutations that avoid the pattern 231 (and, by symmetry, the patterns 132, 213, or 312).

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Kassie Archer, Robert P. Laudone. 2025-05-09. Pattern avoidance in non-crossing and non-nesting permutations. https://arxiv.org/abs/2502.13309

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