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Let $R$ be a discrete valuation ring and $K$ its field of fraction. Let $X$ be a proper $K$-variety, $U$ a dense open and consider an $R$-model $\mathcal{U}$ of $U$. Can we embed $\mathcal{U}$ in a proper $R$-model of $X$?

Nagata's embedding theorem ensures the existence of a compactification for $\mathcal{U}$, but I don't see any way to force its generic fiber to be $X$.

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  • $\begingroup$ It is possible to apply Nagata's theorem to the $R$-scheme obtained by glueing $\mathcal{U}$ and $X$ along $U$. $\endgroup$
    – Olivier Benoist
    Jan 25, 2015 at 12:53
  • $\begingroup$ @OlivierBenoist: right, but you just have to check that this $R$-scheme is separated, e.g. by the valuative criterion. $\endgroup$
    – Laurent Moret-Bailly
    Jan 25, 2015 at 19:50
  • $\begingroup$ Oh, that's great! Thanks you two for the tips! $\endgroup$
    – Piet
    Jan 26, 2015 at 19:18

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