Quotient of Noetherian local ring with $\mathfrak{m}$-primary ideal

artiniancommutative-algebra

Let $A$ be noetherian local with maximal ideal $\mathfrak{m}$ and let $\mathfrak{q}$ be an $\mathfrak{m}$-primary ideal. Then why is $A/\mathfrak{q}$ an artin ring?

$A/\mathfrak{q}$ is noetherian so all we need to do is prove the image of $\mathfrak{m}$ in $A/\mathfrak{q}$ is the only prime ideal (prime and maximal ideals are the same in Artin rings) so that krull dimension of $A/\mathfrak{q}$ is 0. But how do I show this?

This claim is used in the proof of 11.4 of atiyah and macdonald. But I can't see why it is true!

Best Answer

In a Noetherian ring, every ideal contains some power of its radical. Thus there is some $n$ such that $\mathfrak{m}^n\subseteq \mathfrak{q}$. It follows that $(\mathfrak{m}/\mathfrak{q})^n$ is the zero ideal in $A/\mathfrak{q}$. Now, if in a ring $R$ there are some (finitely many) maximal ideals such that their product is $\{0\}$ then $R$ is Noetherian if and only if $R$ is Artin. This is corollary $6.11$ in Atiyah-Macdonald. Since $A/\mathfrak{q}$ is obviously Noetherian, it follows that it is an Artin ring.

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