Claim: the ring $\mathbb{Z}[i]$ is a noetherian ring
My proof
1) $\mathbb{Z}[i]$ is a finitely generated $\mathbb{Z}$-module.
2) $\mathbb{Z}$ is a noetherian ring.
3) Every finitely generated module over a noetherian ring is a noetherian module, hence $\mathbb{Z}[i]$ is a noetherian $\mathbb{Z}$-module.
4) By definition of noetherian module, every $\mathbb{Z}$-submodule of $\mathbb{Z}[i]$ is finitely generated as a $\mathbb{Z}$-module
5) an ideal $\mathfrak{i}$ of $\mathbb{Z}[i]$ is in particular a $\mathbb{Z}$-submodule of $\mathbb{Z}[i]$
6) $\mathfrak{i}=\mathbb{Z}x_1+\ldots +\mathbb{Z}x_n$
7) since $\mathfrak{i}$ is finitely generated as a $\mathbb{Z}$-module, it is also finitely generated as an ideal
Do you think my proof works?
Best Answer
Would you like another proof?
By Hilbert's Theorem $\mathbb{Z}[X]$ is noetherian. Hence $\mathbb{Z}[i]$ is also noetherian as a factor-ring of $\mathbb{Z}[X]$.
Addendum: In fact, here (for one unknown) Hilbert's theorem is not needed.