diff --git a/iii/commalg/04_integrality_finiteness_finite_generation.tex b/iii/commalg/04_integrality_finiteness_finite_generation.tex index 9026e5f..a330413 100644 --- a/iii/commalg/04_integrality_finiteness_finite_generation.tex +++ b/iii/commalg/04_integrality_finiteness_finite_generation.tex @@ -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 \( \mathfrak p \in \Spec A \).