We first prove a lemma on generic flatness:
LEMMA (Generic Flatness) Let $A$ be a noetherian domain, and $B$ a finite type $A$-algebra. Let $M$ be a finite $B$-module. Then there exists an $f \in A, f\neq 0$, such that the localization $M_f$ is a free module over $A_f$.
\begin{proof}
Let $K$ be the fraction field of the domain $A$. Consider the localization at this generic point: $M_K = M \otimes K$
\end{proof}
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