Counterexamples about Infinitely Generated Modules over Commutative Rings

This post is about examples of some nice things that could fail for modules that are not finitely generated (or not finitely presented when the ring is not Noetherian).

1. Nakayama’s Lemma (Krull’s Intersection Theorem)

2. \mathrm{Supp}M =V(\mathrm{ann M}).

3. \mathrm{Hom}_A(M,N)\otimes B= \mathrm{Hom}_B(M\otimes_A B, N\otimes_A B) for B a flat A-module

4. M\otimes _R \hat{R} =\hat{M}

5. Finitely Generated Nil Ideal is Nilpotent

6. Finitely presented flat module is projective

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s