Conjugacy-class parity conjecture for finite 2-groups

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Let π\pi be a finite 22-group and let N◃T⊴W◃πN\triangleleft T\trianglelefteq W\triangleleft\pi be normal subgroups such that π/N\pi/N is cyclic, T/N≅Z/2T/N\cong\mathbb Z/{2}, and π/W≅Z/2\pi/W\cong\mathbb Z/{2}. Let i ⁣:W→πi\colon W\to\pi be inclusion and p ⁣:π→π/Np\colon\pi\to\pi/N the quotient map. Assume that

p∗ ⁣:H4(π;Z/2)→H4(π/N;Z/2)≅Z/2p_*\colon H_4(\pi;\mathbb Z/{2})\to H_4(\pi/N;\mathbb Z/{2})\cong\mathbb Z/{2}

and

(p∘i)∗ ⁣:H2(W;Z/2)→H2(π/N;Z/2)≅Z/2(p\circ i)_*\colon H_2(W;\mathbb Z/{2})\to H_2(\pi/N;\mathbb Z/{2})\cong\mathbb Z/{2}

are nonzero, while

(p∘i)∗ ⁣:H4(W;Z/2)→H4(π/N;Z/2)≅Z/2(p\circ i)_*\colon H_4(W;\mathbb Z/{2})\to H_4(\pi/N;\mathbb Z/{2})\cong\mathbb Z/{2}

is zero. Conjugacy-class parity conjecture. The number of π\pi-conjugacy classes of elements in T−NT-N is odd. The statement is presented as a conjecture motivated by the study of vanishing of κ4′(π)\kappa'_4(\pi); no resolution is supplied in the provided text.

References

Primary source

Ian Hambleton and Ozgun Unlu, “Closed manifold surgery obstructions and the Oozing Conjecture”, arXiv:2602.05003 (2026).

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