Maximal ideals in Artinian ring

3.3k Views Asked by At

It is known that Artinian (commutative) ring has finitely many maximal ideals.

(One proof is by considering finite intersections of maximal ideals, and a chain from it, then using Artinian property of ring and some lemma.)

I have one problem in following arguments given in Mastumuta's Ring theory.

Let $\mathfrak{p}_1,\mathfrak{p}_2\cdots$ be infinite family maximal ideals of Artinian ring $R$.

Then the chain $$\mathfrak{p}_1 \supset \mathfrak{p}_1\mathfrak{p}_2 \supset \cdots$$ is strictly decreasing (why it is strictly decreasing?)

I tried to use Nakayama lemma, but we do not know whether ideals are finitely generated - since at this argument of Matsumuta, it is not known that ideals are finitely generated. (At the end of proof, it is proved that ideals are finitely generated.)

In short, I want to prove that above chain of ideals is strictly decreasing, without assuming them to be finitely generated. How can we prove it?

1

There are 1 best solutions below

3
On BEST ANSWER

If $\mathfrak p_1\cdots \mathfrak p_k=\mathfrak p_1\cdots \mathfrak p_{k-1}$, then $\mathfrak p_1\cap\cdots\cap \mathfrak p_k=\sqrt{\mathfrak p_1\cdots \mathfrak p_k}=\sqrt{\mathfrak p_1\cdots \mathfrak p_{k-1}}=\mathfrak p_1\cap\cdots\cap \mathfrak p_{k-1}$. In other words, $\mathfrak p_k$ is a prime ideal containing $\bigcap_{i=1}^{k-1} \mathfrak p_i$. But this is the case if and only if $\mathfrak p_k\supseteq \mathfrak p_j$ for some $j\le k-1$.