Published online by Cambridge University Press: 05 October 2020
We consider the structures $(\mathbb {Z}; \mathrm {SF}^{\mathbb {Z}})$,
$(\mathbb {Z}; <, \mathrm {SF}^{\mathbb {Z}})$,
$(\mathbb {Q}; \mathrm {SF}^{\mathbb {Q}})$, and
$(\mathbb {Q}; <, \mathrm {SF}^{\mathbb {Q}})$ where
$\mathbb {Z}$ is the additive group of integers,
$\mathrm {SF}^{\mathbb {Z}}$ is the set of
$a \in \mathbb {Z}$ such that
$v_{p}(a) < 2$ for every prime p and corresponding p-adic valuation
$v_{p}$,
$\mathbb {Q}$ and
$\mathrm {SF}^{\mathbb {Q}}$ are defined likewise for rational numbers, and
$<$ denotes the natural ordering on each of these domains. We prove that the second structure is model-theoretically wild while the other three structures are model-theoretically tame. Moreover, all these results can be seen as examples where number-theoretic randomness yields model-theoretic consequences.