The order of the (123, 132)-avoiding stack sort

Let s be West's deterministic stack-sorting map.A well-known result is that every length n permutation is sorted with n -1 iterations of s.In 2020, Defant introduced the notion of highly-sorted permutationspermutations obtained by applying slightly less than n -1 iterations of s.In 2023, Choi & Choi extended this notion to generalized stack-sorting maps s , where we relax the condition of becoming sorted to the analogous condition of becoming periodic with respect to s .While periodicity seems counterintuitive in the context of sorting, it arises naturally in these restrictive forms, where the map is studied as an operator with properties rather than a means to "sort" permutations in the usual sense.In this work, we introduce the notion of minimally-sorted permutations as an antithesis to Defant's highlysorted permutations, and show that the order of the (123, 132)-avoiding stack-sorting map is 2 n-1 2 .

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Publication Details

Journal
Enumerative Combinatorics and Applications
Published
2025-04-04
DOI
https://doi.org/10.54550/eca2025v5s3r18
Primary Topic
Logic, programming, and type systems
Type
article
Field-Weighted Citation Impact
0.00
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article

The order of the (123, 132)-avoiding stack sort

Owen Zhang
Enumerative Combinatorics and Applications
Logic, programming, and type systems
article

The order of the (123, 132)-avoiding stack sort

Owen Zhang
article en

Abstract

Let s be West's deterministic stack-sorting map.A well-known result is that every length n permutation is sorted with n -1 iterations of s.In 2020, Defant introduced the notion of highly-sorted permutationspermutations obtained by applying slightly less than n -1 iterations of s.In 2023, Choi & Choi extended this notion to generalized stack-sorting maps s , where we relax the condition of becoming sorted to the analogous condition of becoming periodic with respect to s .While periodicity seems counterintuitive in the context of sorting, it arises naturally in these restrictive forms, where the map is studied as an operator with properties rather than a means to "sort" permutations in the usual sense.In this work, we introduce the notion of minimally-sorted permutations as an antithesis to Defant's highlysorted permutations, and show that the order of the (123, 132)-avoiding stack-sorting map is 2 n-1 2 .

Enumerative Combinatorics and ApplicationsVol. 5(3)
Yale University (US)
Openalex Percentile: Top 96%
Logic, programming, and type systems
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