Is the set $\left\{(x, y) \in \mathbb{Q}_{>0}^2 \, : \, \frac{x}{y} \in 2\mathbb{N} - 1\right\}$ definable in FO($\mathbb{Q}, +, \leq$).
Definability in FO($\mathbb{Q}, +, \leq$)
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logic
model-theory
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0Thoughts? Motivations? – 2012-10-27