HNN extensions of free groups with equal associated subgroups of finite index: polynomial time word problem

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Hauptverfasser: Shen, Hanwen, Ushakov, Alexander
Format: Preprint
Veröffentlicht: 2025
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author Shen, Hanwen
Ushakov, Alexander
author_facet Shen, Hanwen
Ushakov, Alexander
contents Let $G=F\ast_φt$ be an HNN extension of a free group $F$ with two equal associated normal subgroups $H_1 = H_2$ of finite index. We prove that the word problem in $G$ is decidable in polynomial time. This result extends to the case where the subgroups $H_1=H_2$ are not normal, provided that the isomorphism $φ:H_1\to H_2$ satisfies an additional condition described in Section 5.
format Preprint
id arxiv_https___arxiv_org_abs_2510_03801
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle HNN extensions of free groups with equal associated subgroups of finite index: polynomial time word problem
Shen, Hanwen
Ushakov, Alexander
Group Theory
Computational Complexity
Combinatorics
Let $G=F\ast_φt$ be an HNN extension of a free group $F$ with two equal associated normal subgroups $H_1 = H_2$ of finite index. We prove that the word problem in $G$ is decidable in polynomial time. This result extends to the case where the subgroups $H_1=H_2$ are not normal, provided that the isomorphism $φ:H_1\to H_2$ satisfies an additional condition described in Section 5.
title HNN extensions of free groups with equal associated subgroups of finite index: polynomial time word problem
topic Group Theory
Computational Complexity
Combinatorics
url https://arxiv.org/abs/2510.03801