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Let $A$ be a local ring. Say a monic $f\in A[x]$ is unramifiable if it admits a simple root in its universal splitting algebra (equivalently, it admits a simple root in any ring over which it splits). Say a local ring is separably closed if every unramifiable polynomial admits a simple root. By a result of Wraith, the separably closed local rings are precisely the strictly Henselian ones.

A separably closed field is precisely one without separable extensions.

Is it also true that (injective?) separable algebras over a separably closed local ring are isomorphisms?

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  • $\begingroup$ What do you mean by "splitting" and "simple root" over a general ring? $\endgroup$ Commented Sep 28, 2021 at 6:32
  • $\begingroup$ @LaurentMoret-Bailly "split" = is a product of degree one polynomials. "simple root" = root at which the formal derivative is invertible. $\endgroup$
    – Arrow
    Commented Sep 28, 2021 at 9:15

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