Lemma 10.137.3. Let $R \to S$ be a smooth ring map. Any localization $S_ g$ is smooth over $R$. If $f \in R$ maps to an invertible element of $S$, then $R_ f \to S$ is smooth.

Proof. By Lemma 10.134.13 the naive cotangent complex for $S_ g$ over $R$ is the base change of the naive cotangent complex of $S$ over $R$. The assumption is that the naive cotangent complex of $S/R$ is $\Omega _{S/R}$ and that this is a finite projective $S$-module. Hence so is its base change. Thus $S_ g$ is smooth over $R$.

The second assertion follows in the same way from Lemma 10.134.11. $\square$

## Comments (1)

Comment #718 by Keenan Kidwell on

The proof of the second part repeats the argument for the proof of 07BS. Maybe just cite 07BS (it seems like it was given for just this result).

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