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Andrei Jaikin
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Exact sequences with two FL-modules

Let $R$ be a ring. An $R$-module $M$ is called FL (FP) if it has a finite resolution consisiting of finitely generated free (projective) modules.

Given an exact sequence of $R$-modules, $0\to M_1\to M_2\to M_3\to 0$, if two of the modules $M_1$, $M_2$ or $M_3$ are FP, then the third is FP as well. This follows, for example, from Proposition 1.4 and Proposition 4.1b of

Bieri, Robert Homological dimension of discrete groups. Queen Mary College Mathematics Notes. Queen Mary College, Mathematics Department, London, 1976.

My question is

If two of the modules $M_1$, $M_2$ or $M_3$ are FL, is it true that the third one is also FL?

Andrei Jaikin
  • 1.4k
  • 1
  • 9
  • 13