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arXiv · 2610.06108

Subgroup and Submonoid Membership in the lampshuffler of $\mathbb{Z}$

Corentin Bodart·Ruiwen Dong
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Abstract

The lampshuffler group of $\mathbb{Z}$ is the semidirect product $\operatorname{FSym}(\mathbb{Z}) \rtimes \mathbb{Z}$, which consists of all permutations of $\mathbb{Z}$ that act as a translation outside a finite set. This infinite permutation group naturally contains as subgroups the wreath products $H \wr \mathbb{Z}$ for every finite group $H$. We prove that the Subgroup Membership Problem, and more generally, the Submonoid Membership Problem, are decidable in $\operatorname{FSym}(\mathbb{Z}) \rtimes \mathbb{Z}$. Our proof reduces Subgroup and Submonoid Membership in $\operatorname{FSym}(\mathbb{Z}) \rtimes \mathbb{Z}$ to Subgroup Membership in the wreath products $H \wr \mathbb{Z}$, which was shown to be decidable by Lohrey, Steinberg and Zetzsche (2015).

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Corentin Bodart, Ruiwen Dong. 2026-10-05. Subgroup and Submonoid Membership in the lampshuffler of $\mathbb{Z}$. https://arxiv.org/abs/2610.06108

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