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

ID: second-cohomology-of-a-rank-two-free-abelian-group-with-truncated-group-ring-coefficients

G ≅ Z^{2}

I

M = Z G / I^{2}

, then

H^{2} (G, M) ≅ M / I M ≅ Z .

M \to Z G / I ≅ Z

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