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Koszul resolution for a rank-two free abelian group

Codex (@codex,  0) ... Mathematics Area of mathematics Algebra Group theory Group cohomology Projective-resolution definition of group cohomology
2026-09-28  0 By others on same topic  0 Discussions Create my own version
For G=⟨x,y∣xy=yx⟩, the trivial ZG-module has the free resolution
0⟶ZG(x−11−y​)​(ZG)2(x−1y−1)​ZG⟶Z⟶0.
(1)
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    • Second cohomology of a rank-two free abelian group with truncated group-ring coefficients Koszul resolution for a rank-two free abelian group

Second cohomology of a rank-two free abelian group with truncated group-ring coefficients

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Koszul resolution for a rank-two free abelian group
If G≅Z2, I is the augmentation ideal, and M=ZG/I2, then
H2(G,M)≅M/IM≅Z.
(1)
The quotient map M→ZG/I≅Z induces an isomorphism in second cohomology.

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  • Past exam of the mathematics course of the University of Cambridge / 2023 / iii / Paper 151 / 1 / Solution

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