Isomorphisms of unit distance graphs of layers

TL;DR

This paper investigates the isomorphism classes of unit distance graphs of layered Euclidean spaces, proving they are uniquely determined by layer width and that automorphisms are isometries, extending classical geometric theorems.

Contribution

It establishes that unit distance graphs of different layers are non-isomorphic and that automorphisms of these graphs are isometries, generalizing known results to higher dimensions.

Findings

Unit distance graphs of different layers are non-isomorphic.

Automorphisms of these graphs are isometries.

Results extend classical theorems like Beckman-Quarles to layered spaces.

Abstract

For any $\varepsilon \in (0,+\infty)$, consider the metric spaces $\mathbb{R} \times [0,\varepsilon]$ in the Euclidean plane named layers or strips. B. Baslaugh in 1998 found the minimal width $\varepsilon \in (0,1)$ of a layer such that its unit distance graph contains a cycle of a given odd length $k$. The first of the main results of this paper is the fact that the unit distance graphs of two layers $\mathbb{R} \times [0,\varepsilon_1], \mathbb{R} \times [0,\varepsilon_2]$ are non-isomorphic for any different values $\varepsilon_1,\varepsilon_2 \in (0,+\infty)$. We also get a multidimensional analogue of this theorem. For given $n,m \in \mathbb{N}, p \in (1,+\infty), \varepsilon \in (0,+\infty)$, we say that the metric space on $\mathbb{R}^n \times [0,\varepsilon]^m$ with the metric space distance generated by $l_p$-norm in $\mathbb{R}^{n+m}$ is a layer $L(n,m,p,\varepsilon)$. We show that the unit distance graphs of layers $L(n,m,p,\varepsilon_1), L(n,m,p,\varepsilon_2)$ are non-isomorphic for $\varepsilon_1 \neq \varepsilon_2$. The third main result of this paper is the theorem that, for $n \geq 2, \varepsilon > 0$, any automorphism $\phi$ of the unit distance graph of layer $L = L(n,1,2,\varepsilon) = \mathbb{R}^n \times [0,\varepsilon]$ is an isometry. This is related to the Beckman-Quarles theorem of 1953, which states that any unit-preserving mapping of $\mathbb{R}^n$ is an isometry, and to the rational analogue of this theorem obtained by A. Sokolov in 2023.