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I know if $E/F$ is a finitely generated algebraic extension of fields, then $E/F$ is separable iff the Kahler differential $\Omega_{E/F}=0$.

Question: I wonder if we only assume that $E/F$ is algebraic without finitely generated, and $\Omega_{E/F}=0$, then is $E/F$ separable?

Edit: This question doesn't solve my question, since the answer there uses the assumption that $E/F$ is finitely generated.

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Kahler differentials commute with colimits, and any algebraic extension is the colimit of its finite subextensions (more generally, any field extension is the colimit of its finitely generated subextensions). Applying the result in the finite case, we have your desired result as the colimit of a diagram of zero modules is zero.

KReiser
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