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arXiv · 1807.07748

On quasi-purity of the branch locus

Alexander Schmidt
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Abstract

Let $k$ be a field, $K/k$ finitely generated and $L/K$ a finite, separable extension. We show that the existence of a $k$-valuation on $L$ which ramifies in $L/K$ implies the existence of a normal model $X$ of $K$ and a prime divisor $D$ on the normalization $X_L$ of $X$ in $L$ which ramifies in the scheme morphism $X_L \rightarrow X$. Assuming the existence of a regular, proper model $X$ of $K$, this is a straight-forward consequence of the Zariski-Nagata theorem on the purity of the branch locus. We avoid assumptions on resolution of singularities by using M. Temkin's inseparable local uniformization theorem.

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Alexander Schmidt. 2018-07-20. On quasi-purity of the branch locus. https://doi.org/10.1007/s00229-018-1096-y

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