In this post, if $I$ is a finitely generated ideal of a commutative ring $A$ with 1 such that $I^2=I$, then we know $I$ is principal. To answer this question without using Nakayama lemma, I have a complicated method, first reduce to Noetherian case, then apply Krull intersection theorem(Artin Rees lemma) (In fact, by this method we can induce Nakayama's lemma.) Finiteness is essential, see :
Let $A=\prod_{i\in \mathbb{N}}\mathbb{Z}/2\mathbb{Z}$, $I=\bigoplus_{i\in\mathbb{N}}\mathbb{Z}/2\mathbb{Z}$, $\mathfrak{m}$ be a maximal ideal containing $I$. Then $\mathfrak{m}^2=\mathfrak{m}$, $I^2=I$, but neither $I$ nor $\mathfrak{m}$ can be finitely generated. Unfortunately, $A$ is an absolutely flat ring, localized at any prime will become a field.
I am interesting to find some examples as follow required.
- Find a local ring $(A,\mathfrak{m})$, such that $\cap_{n\in\mathbb{N}}\mathfrak{m}^n\neq 0$.
- Furthermore, find $A$ satisfying (1) such that $A$ is a domain and $\mathfrak{m}$ is finitely generated .
- Find an (integral) local ring $(A,\mathfrak{m})$ with $\mathfrak{m}^2=\mathfrak{m}\neq 0$