Finitely generated projective resolution

abstract-algebrahomological-algebraprojective-module

Let $K$ be a field, $A$ be a finite dimensional $K$-algebra and $M$ be a finitely generated $A$-module. Is it true that $M$ admits a projective resolution by finitely generated projective $A$-modules?

Best Answer

As $A$ is a finite algebra over $K$ it is noetherian. As $M$ is finitely generated there is a surjection $A^{\oplus n} \longrightarrow M$. $A^{\oplus n}$ is noetherian as $A$ is. Let $N$ be the kernel of this map. By noetherianness, it is finitely generated, so there is a surjection $A^{\oplus m} \longrightarrow N$ and hence an exact sequence $A^{\oplus m} \longrightarrow A^{\oplus n} \longrightarrow M \longrightarrow 0$. Repeat this process to get a projective (in fact free) resolution by finitely generated modules. Note that we didn't need the full strength of the assumption that $A$ is finite over $K$ - only that it was noetherian.

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