vol. 28:1, Permutation Patterns 2025

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1. Stack-sorting preimages and 0-1-trees

Bona, Miklos.

We define a class of partially labeled trees and use them to find simple proofs for two recent enumeration results of Colin Defant concerning stack-sorting preimages of permutation classes.

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2. A Pollak Proof for the Number of Weakly Increasing Parking Functions

Harris, Pamela E. ; Mori, J. Carlos Martínez ; Wilson, Alexander N..

We develop a circular-street argument, in the style of Pollak, to obtain a new proof that there are $C_n = \frac{1}{n+1}\binom{2n}{n}$ weakly increasing parking functions of length $n \geq 1$, where $C_n$ is the $n$th Catalan number.

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