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Final fixes
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Signed-off-by: zeramorphic <[email protected]>
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zeramorphic committed Jun 3, 2024
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4 changes: 2 additions & 2 deletions iii/commalg/04_integrality_finiteness_finite_generation.tex
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Expand Up @@ -609,8 +609,8 @@ \subsection{Cohen--Seidenberg theorems}
\[ \mathfrak q B_{\mathfrak p} \cap A_{\mathfrak p} = S^{-1} \mathfrak q \cap S^{-1} A = S^{-1} (\mathfrak q \cap A) = S^{-1} \mathfrak p = \mathfrak p A_{\mathfrak p} \]
Similarly, \( \mathfrak q' B_{\mathfrak p} \cap A_{\mathfrak p} = \mathfrak p A_{\mathfrak p} \), which is a maximal ideal of \( A_{\mathfrak p} \).
As \( A \subseteq B \) is an integral extension, \( A_{\mathfrak p} \subseteq B_{\mathfrak p} \) is also an integral extension.
Recall that the contraction of a maximal ideal is maximal in such an extension.
Now, \( \mathfrak q B_{\mathfrak p} \subseteq \mathfrak q' B_{\mathfrak p} \) are maximal ideals of \( B_{\mathfrak p} \), so they must coincide.
Recall that the if the contraction of a prime ideal is maximal in an integral extension, the prime ideal was maximal.
Thus, \( \mathfrak q B_{\mathfrak p} \subseteq \mathfrak q' B_{\mathfrak p} \) are maximal ideals of \( B_{\mathfrak p} \), so they must coincide.
\end{proof}
\begin{proposition}[lying over]
Let \( A \subseteq B \) be an integral extension of rings, and let \( \mathfrak p \in \Spec A \).
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