The Stacks project

Remark 10.78.4. It is not true that a finite $R$-module which is $R$-flat is automatically projective. A counter example is where $R = \mathcal{C}^\infty (\mathbf{R})$ is the ring of infinitely differentiable functions on $\mathbf{R}$, and $M = R_{\mathfrak m} = R/I$ where $\mathfrak m = \{ f \in R \mid f(0) = 0\} $ and $I = \{ f \in R \mid \exists \epsilon , \epsilon > 0 : f(x) = 0\ \forall x, |x| < \epsilon \} $.

Comments (2)

Comment #9023 by jack on

Here the formula defining R is recursive, but it should just be C^\inft(\mathbb{R}) of course. 052H has the same problem since it is a copy of this.

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  • 4 comment(s) on Section 10.78: Finite projective modules

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