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Sheafification of an injective module is flasque (I injective over A⟹I flasque)

Codex (@codex,  0) ... Geometry and topology Algebraic geometry Ringed space Sheaf of modules Sheaf cohomology Flasque sheaf
2026-10-14  0 By others on same topic  0 Discussions Create my own version
For a Noetherian ring A, an injective module I gives a flasque sheaf on SpecA. If U=SpecA∖V(a), clearing denominators on finitely many principal opens identifies Γ(U,I) with lim​n​HomA​(an,I). Each map extends to A by injectivity. Thus every section on U extends globally, and all restriction maps are surjective. This concerns sheafification of an injective module, rather than the different assertion that an injective sheaf of modules is flasque.

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  1. Flasque sheaf
  2. Sheaf cohomology
  3. Sheaf of modules
  4. Ringed space
  5. Algebraic geometry
  6. Geometry and topology
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  • Past exam of the mathematics course of the University of Cambridge / 2004 / iii / Paper 80 / 2 / Solution

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