Two typos in more-algebra

Thanks to Yijin Wang
https://stacks.math.columbia.edu/tag/07PD#comment-6542
https://stacks.math.columbia.edu/tag/07PD#comment-6543
https://stacks.math.columbia.edu/tag/07PD#comment-6544

more-algebra.tex

@@ -11498,11 +11498,11 @@ \section{Regularity and derivations}
 see that $A$ is J-0 by Lemma \ref{lemma-J-0-goes-up}.
 If not, then $K = M[z]/(z^p - b)$ for some $b \in B$
 which is not a $p$th power in $M$. By Lemma \ref{lemma-find-D}
-we can find a derivation $D : B \to B$ with $D(f) \not = 0$.
+we can find a derivation $D : B \to B$ with $D(b) \not = 0$.
 Applying Lemma \ref{lemma-degree-p-extension-regular}
 we see that $A_\mathfrak p$ is regular for any prime
 $\mathfrak p$ of $A$ lying over a regular prime of $B$
-and not containing $D(f)$. As $B$ is J-0 we conclude $A$ is too.
+and not containing $D(b)$. As $B$ is J-0 we conclude $A$ is too.
 \end{proof}
 
 \begin{proposition}