Abstract
Given a finite nonempty set of primes S, we build a graph \({\mathcal{G}}\) with vertex set \({\mathbb{Q}}\) by connecting \({x, y \in \mathbb{Q}}\) if the prime divisors of both the numerator and denominator of x − y are from S. In this paper we resolve two conjectures posed by Ruzsa concerning the possible sizes of induced nondegenerate cycles of \({\mathcal{G}}\), and also a problem of Ruzsa concerning the existence of subgraphs of \({\mathcal{G}}\) which are not induced subgraphs.
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Ćustić, A., Hajdu, L., Kreso, D. et al. On conjectures and problems of Ruzsa concerning difference graphs of S-units. Acta Math. Hungar. 146, 391–404 (2015). https://doi.org/10.1007/s10474-015-0513-x
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DOI: https://doi.org/10.1007/s10474-015-0513-x