Lagmental Vicfred

Artinian Rings Have Krull Dimension Zero by Vicfred

Last updated: Tue 13 July 2021

In a commutative Artinian ring every prime ideal is maximal and only finitely many maximal ideals occur. The formulas are more useful when each symbol has a job rather than merely decorating the theorem.

Statement

A ring \(A\) is Noetherian when ascending chains of ideals stabilise. Equivalently, every ideal \(I\triangleleft A\) is finitely generated, so finite data controls all later ideal growth.

$$ I_1\supseteq I_2\supseteq I_3\supseteq\cdots $$

A reliable calculation names domain and codomain. The notation \(\mathsf{data}\mapsto\mathsf{claim}\) is harmless only after both \(\operatorname{dom}\) and \(\operatorname{cod}\) have been fixed.

$$ A\ \text{Artinian}\Longrightarrow\dim A=0 $$

Worked algebra

The computation below is not a second theorem. It is a checksum for the definitions and a place to inspect the difficult LaTeX at full size.

$$ A\cong A_{\mathfrak m_1}\times\cdots\times A_{\mathfrak m_r},\qquad \operatorname{Spec}A=\{\mathfrak m_1,\ldots,\mathfrak m_r\} $$

Conceptual compression

The invariant statement is the one that does not depend on a convenient choice of coordinates, representatives, basis, or enumeration.

$$ \begin{aligned} \mathsf{D}\;&:\quad I_1\supseteq I_2\supseteq I_3\supseteq\cdots,\\[5pt] \mathsf{C}\;&:\quad A\ \text{Artinian}\Longrightarrow\dim A=0. \end{aligned} $$

Caveat

Noetherian does not mean finite, Artinian, or a domain. Each additional adjective imposes a different chain condition or multiplicative property.

$$ \boxed{\begin{gathered} \text{compact conclusion}\\[-2pt] A\ \text{Artinian}\Longrightarrow\dim A=0 \end{gathered}} $$

The notation is dense, but it is doing honest work: every delimiter records scope and every index records dependence. Removing one should require a mathematical reason.

This article was posted on Tue 14 May 2013. Facts and circumstances may have changed since publication.
Please contact me before jumping to conclusions if something seems wrong or unclear.