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arXiv · 2407.15118

A Cobham theorem for scalar multiplication

Philipp Hieronymi·Sven Manthe·Chris Schulz
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Abstract

Let $\alpha,\beta \in \mathbb{R}_{>0}$ be such that $\alpha,\beta$ are quadratic and $\mathbb{Q}(\alpha)\neq \mathbb{Q}(\beta)$. Then every subset of $\mathbb{R}^n$ definable in both $(\mathbb{R},{<},+,\mathbb{Z},x\mapsto \alpha x)$ and $(\mathbb{R},{<},+,\mathbb{Z},x\mapsto \beta x)$ is already definable in $(\mathbb{R},{<},+,\mathbb{Z})$. As a consequence we generalize Cobham-Semenov theorems for sets of real numbers to $\beta$-numeration systems, where $\beta$ is a quadratic irrational.

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Philipp Hieronymi, Sven Manthe, Chris Schulz. 2024-07-21. A Cobham theorem for scalar multiplication. https://arxiv.org/abs/2407.15118

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