Cohomological collapse conjecture for finite cyclic semidirect products

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Let GG be a finite cyclic group and let LL be a finitely generated ZG\mathbb ZG-lattice. For the semidirect product extension

1⟶L⟶G⋊L⟶G⟶1,1\longrightarrow L\longrightarrow G\rtimes L\longrightarrow G\longrightarrow 1,

consider its Lyndon–Hochschild–Serre spectral sequence. Cohomological collapse conjecture. For every k≥0k\geq 0,

Hk(G⋊L,Z)=⨁i+j=kHi(G,Hj(L,Z)).H^k(G\rtimes L,\mathbb Z)=\bigoplus_{i+j=k}H^i\bigl(G,H^j(L,\mathbb Z)\bigr).

This equality is the asserted consequence of collapse at E2E_2 for all finite cyclic groups and finitely generated integral lattices; the source reports collapse in all examples considered but does not establish the general statement.

References

Primary source

Alejandro Adem, Jianquan Ge, Jianzhong Pan and Nansen Petrosyan, “Compatible Actions and Cohomology of Crystallographic Groups”, arXiv:0704.1823 (2007).

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