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33 votes
3 answers
6k views

(co)homology of symmetric groups

Let $S_n=\{\text{bijections }[n]\to[n]\}$ be the n-th symmetric group. Its (co)homology will be understood with trivial action. What are the $\mathbb{Z}$-modules $H_k(S_n;\mathbb{Z})$? Using GAP, we ...
Leo's user avatar
  • 1,589
51 votes
1 answer
8k views

What is Atiyah's topological formulation of the odd order theorem?

Here is a quote from an article by Daniel Gorenstein on the history of the classification of finite simple groups (available here). During that year in Harvard, Thompson began his monumental ...
spin's user avatar
  • 2,821
17 votes
1 answer
1k views

A finite 2-group containing the dihedral group of order 16?

The dihedral group $D_{16}$ of order 16 has a presentation $D_{16}= \langle a,t \ | \ a^2=t^8=atat=e\rangle$. Question: Does there exist a finite 2-group $G$ containing $D_{16}$ as a subgroup, and ...
Nicholas Kuhn's user avatar
17 votes
1 answer
575 views

Group cochains invariant under the action of the symmetric group

Let $G$ be a finite group and $A$ an abelian group. Recall the cochain groups $$ C^k = \{f: G^k \to A\} $$ and the coboundary map $$ \delta : C^k \to C^{k+1} $$ $$ (\delta f)(g_1, \ldots, ...
Kevin Walker's user avatar
  • 12.8k
5 votes
1 answer
384 views

Which groups have undetectable third U(1)-cohomology?

Let $G$ be a finite group. A categorical Schur detector for $G$ is a set $\mathcal{S}$ of proper subgroups $S \subsetneq G$ such that the total restriction map $$ \mathrm{rest}_{\mathcal{S}} : \mathrm{...
Theo Johnson-Freyd's user avatar