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## Group cohomology of elementary abelian group of prime-square order

, 21:34, 24 October 2011
Over the integers
===Over the integers===
The homology groups below can be computed using the homology groups for the [[group of prime order]] (see [[group cohomology of finite cyclic groups]]) and combining it with the [[Kunneth formula for group homology]]. $H_q(\mathbb{Z}/p\mathbb{Z} \oplus \mathbb{Z}/p\mathbb{Z};\mathbb{Z}) = \left\lbrace \begin{array}{rl} (\mathbb{Z}/p\mathbb{Z})^{(q + 3)/2} & \qquad q = 1,3,5,\dots \\ (\mathbb{Z}/p\mathbb{Z})^{q/2}, & \qquad q = 2,4,6,\dots \\ \mathbb{Z}, & \qquad q = 0 \\\end{array}\right.$
The even and odd cases can be combined giving the following alternative description:
$H_q(\mathbb{Z}/p\mathbb{Z} \oplus \mathbb{Z}/p\mathbb{Z};\mathbb{Z}) = \left\lbrace \begin{array}{rl} (\mathbb{Z}/p\mathbb{Z})^{q/2 + 3(1 - (-1)^q)/4}, & \qquad q > 0 \\ \mathbb{Z}, & \qquad q = 0 \\\end{array}\right.$

The first few homology groups are given below:
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