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28 votes
4 answers
3k views

Yoga of six functors for group representations?

I'm trying to understand how the six functor philosophy applies to representation theory. Consider the category of classifying stacks $BG$ (assume $G$ discrete for simplicity). To every stack we can ...
3 votes
1 answer
565 views

Finiteness of cohomology group

Suppose $G$ is a finite Galois group, and $M$ is an infinite $G$-module. When can I say that $H^1(G, M)$ is finite? I know this not true in general. Is it true under certain assumptions on $M$? To be ...
4 votes
0 answers
192 views

Extended double 2-cocycle conditions: Mathematical structure behind?

Note: For experts, to save your time, you can just read the highlighted texts and Eqs directly. The ordinary group 2-cocycle condition: Let us remind the usual so-called homogeneous group 2-cocycle $...
4 votes
0 answers
76 views

Minimal rank of a permutation resolution of a $G$-lattice

Let $G$ be a finite group. By a $G$-lattice I mean a finitely generated free abelian group $L$ with an action of $G$. One says that $L$ is a permutation lattice if $L$ has a $\mathbb{Z}$-basis ...