The fp-injective module conjecture

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Let AA be a ring, and let Fpinj⁡A\operatorname{Fpinj} A be the category of fp-injective AA-modules. Write K(Inj⁡A)\mathbf K(\operatorname{Inj} A) for the homotopy category of complexes of injective AA-modules, K(Fpinj⁡A)\mathbf K(\operatorname{Fpinj} A) for the homotopy category of complexes in Fpinj⁡A\operatorname{Fpinj} A, and D(Fpinj⁡A)\mathbf D(\operatorname{Fpinj} A) for its derived category. If AA is coherent, also write Dpur(Mod⁡A)\mathbf D_{\mathrm{pur}}(\operatorname{Mod} A) for the pure derived category, D(Fpinj⁡A)c\mathbf D(\operatorname{Fpinj} A)^c for the compact objects, and Db(mod⁡A)\mathbf D^b(\operatorname{mod} A) for the bounded derived category of finitely presented AA-modules. The fp-injective module conjecture. For every ring AA, the composite

K(Inj⁡A)→incK(Fpinj⁡A)→canD(Fpinj⁡A)\mathbf K(\operatorname{Inj} A)\xrightarrow{\mathrm{inc}}\mathbf K(\operatorname{Fpinj} A)\xrightarrow{\mathrm{can}}\mathbf D(\operatorname{Fpinj} A)

is an equivalence. If AA is coherent, then D(Fpinj⁡A)\mathbf D(\operatorname{Fpinj} A) is compactly generated, and the composite

D(Fpinj⁡A)→Dpur(Mod⁡A)→D(Mod⁡A)\mathbf D(\operatorname{Fpinj} A)\to\mathbf D_{\mathrm{pur}}(\operatorname{Mod} A)\to\mathbf D(\operatorname{Mod} A)

induces an equivalence

D(Fpinj⁡A)c→∼Db(mod⁡A).\mathbf D(\operatorname{Fpinj} A)^c\xrightarrow{\sim}\mathbf D^b(\operatorname{mod} A).

This conjecture extends analogous results for flat modules and predicts that injective resolutions model the derived category of fp-injective modules. Its general categorical form is stated in terms of exact functor categories, but the source provides no resolution of either formulation.

References

Primary source

Henning Krause, “Approximations and adjoints in homotopy categories”, arXiv:1005.0209 (2010).

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