Timeline for How many values of a group cocycle are required to know its cohomology class?

10 events

when toggle format	what		by	license	comment
Sep 13 at 11:23	comment	added	Achim Krause		You can also restrict to values from a $p$-Sylow subgroup to determine the $p$-local part of the cohomology class, by Cartan-Eilenbergs stable element formula (and do this for every $p$ to fully determine it).
Sep 13 at 11:16	history	edited	Mikhail Borovoi	CC BY-SA 4.0	The title edited; changed H^n to Z^n for the grop of n-cocycles.
Sep 12 at 10:45	comment	added	Eric S.		My memory is that the Handbook of Computational Group Theory suggests that one can restrict to a generating set in one of the variables of the cocycle, but otherwise needs to know all the values for the other input.
Sep 12 at 10:22	history	edited	Max Lonysa Muller	CC BY-SA 4.0	Fixed grammar
Sep 12 at 6:16	history	edited	Yarden Sheffer	CC BY-SA 4.0	corrected $[\varphi]$ to be "cohomology class"
Sep 12 at 6:15	comment	added	Yarden Sheffer		@Mikhail Borovoi might have been a slight abuse of notation. I mean that $\varphi$ is a cocycle, belonging to some unknown cohomology class $[\varphi]$. Added a small edit, hope it clarifies. For the second Q, yes, with the usual group action (I guess the question makes sense for any $G$-module)
Sep 11 at 13:55	comment	added	Mikhail Borovoi		And by $U(1)$, do you mean $\{z\in {\mathbb C}^*\ \|\ z\bar z=1\}$ ?
Sep 11 at 13:52	comment	added	Mikhail Borovoi		By $\varphi\in H^n(G,U(1))$, do you mean a cocycle or a cohomology class?
Sep 11 at 13:45	history	edited	Mikhail Borovoi		edited tags
Sep 9 at 15:08	history	asked	Yarden Sheffer	CC BY-SA 4.0