diff --git a/iii/commalg/04_integrality_finiteness_finite_generation.tex b/iii/commalg/04_integrality_finiteness_finite_generation.tex index 53e2502..9026e5f 100644 --- a/iii/commalg/04_integrality_finiteness_finite_generation.tex +++ b/iii/commalg/04_integrality_finiteness_finite_generation.tex @@ -598,7 +598,7 @@ \subsection{Cohen--Seidenberg theorems} Suppose that \( \mathfrak q \) and \( \mathfrak q' \) contract to the same prime ideal \( \mathfrak p = \mathfrak q \cap A = \mathfrak q' \cap A \) of \( A \), and that \( \mathfrak q \subseteq \mathfrak q' \). Then \( \mathfrak q = \mathfrak q' \). \end{proposition} -We will write \( B_{\mathfrak p} \) for \( (A \setminus \mathfrak p)^{-1} B \), but this is not in general a ring. +In this section, we will write \( B_{\mathfrak p} \) to abbreviate \( (A \setminus \mathfrak p)^{-1} B \). \begin{proof} Define \( S = A \setminus \mathfrak p \). Then \( \mathfrak q \) and \( \mathfrak q' \) are prime ideals of \( B \) not intersecting \( S \). diff --git a/iii/commalg/07_dimension_theory.tex b/iii/commalg/07_dimension_theory.tex index d5b296b..89c39b5 100644 --- a/iii/commalg/07_dimension_theory.tex +++ b/iii/commalg/07_dimension_theory.tex @@ -174,15 +174,15 @@ \subsection{Dimension theory of local Noetherian rings} Let \( \mathfrak q \) be an \( \mathfrak m \)-primary ideal of \( A \), generated by \( x_1, \dots, x_s \) where \( s = \delta(\mathfrak q) \). Then - \[ G_{\mathfrak q}(A) = \faktor{A}{\mathfrak q} \oplus \faktor{\mathfrak q}{\mathfrak q^2} \oplus \oplus_{n \geq 2} \faktor{\mathfrak q^n}{\mathfrak q^{n+1}} \] + \[ G_{\mathfrak q}(A) = \faktor{A}{\mathfrak q} \oplus \faktor{\mathfrak q}{\mathfrak q^2} \oplus \bigoplus_{n \geq 2} \faktor{\mathfrak q^n}{\mathfrak q^{n+1}} \] The first factor \( \faktor{A}{\mathfrak q} \) is Artinian, and the images of \( x_1, \dots, x_s \) generate \( G_{\mathfrak q}(A) \) as an \( \faktor{A}{\mathfrak q} \)-algebra, where the \( x_i \) are of degree 1. Then \( \ell\qty(\faktor{\mathfrak q^n}{\mathfrak q^{n+1}}) < \infty \). From the theorem on Hilbert polynomials, \( \ell\qty(\faktor{\mathfrak q^n}{\mathfrak q^{n+1}}) \) is a polynomial in \( n \) of degree at most \( \delta(\mathfrak q) - 1 \), for sufficiently large \( n \). Fix some \( \mathfrak m \)-primary ideal \( \mathfrak q_0 \) such that \( \delta(\mathfrak q_0) = \delta(A) \). We consider two special cases: \( \mathfrak q = \mathfrak q_0 \) and \( \mathfrak q = \mathfrak m \). - For \( \mathfrak q \), we have - \[ \deg \ell\qty(\faktor{\mathfrak q_0^n}{\mathfrak q^0_{n+1}}) \leq \delta(A) - 1 \] + For \( \mathfrak q_0 \), we have + \[ \deg \ell\qty(\faktor{\mathfrak q_0^n}{\mathfrak q_0^{n+1}}) \leq \delta(A) - 1 \] As \[ \ell\qty(\faktor{A}{\mathfrak q_0^n}) = \sum_{i=0}^{n-1} \ell\qty(\faktor{\mathfrak q_0^i}{\mathfrak q_0^{i+1}}) \] we have @@ -190,7 +190,7 @@ \subsection{Dimension theory of local Noetherian rings} For \( \mathfrak m \), \[ \deg \ell\qty(\faktor{\mathfrak m^n}{\mathfrak m^{n+1}}) = d(G_{\mathfrak m}(A)) - 1 \] and hence - \[ \deg \ell\qty(\faktor{A}{\mathfrak m^n}) = d(G_{\mathfrak m})(A) \] + \[ \deg \ell\qty(\faktor{A}{\mathfrak m^n}) = d(G_{\mathfrak m}(A)) \] Now, there exists \( t \geq 1 \) such that \( \mathfrak m^t \subseteq \mathfrak q_0 \subseteq \mathfrak m \). Then @@ -198,7 +198,7 @@ \subsection{Dimension theory of local Noetherian rings} But all of these terms are eventually polynomial, and the degrees of the left-hand and right-hand sides are the same, so we must have \( \ell\qty(\faktor{A}{\mathfrak q_0^n}) = \ell\qty(\faktor{A}{\mathfrak m^n}) \). \begin{proposition} - \( \delta(A) \geq d(G_{\mathfrak m})(A) \) + \( \delta(A) \geq d(G_{\mathfrak m}(A)) \). \end{proposition} \begin{proof} \[ \delta(A) = \delta(\mathfrak q_0) \geq \deg \ell\qty(\faktor{A}{\mathfrak q_0^n}) = \deg \ell\qty(\faktor{A}{\mathfrak m^n}) = d(G_{\mathfrak m}(A)) \]