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Dec 8, 2010 at 16:48 comment added Mark Grant If you wanted examples with non-trivial differentials, I think you would need all isotropy groups $G_x$ to be proper subgroups of $G$, but sadly I'm no expert. And of course in the previous comment I meant $E^2_{*,*}=H_*(G,H_*(X))$!
Dec 8, 2010 at 16:43 comment added Mark Grant The only way I know of computing $H_*^G(X)=H_*(EG\times_G X)$ is by looking at the Leray-Serre spectral sequence of the Borel fibration $X\to EG\times_G X\to BG$. I think in both these cases all differentials are trivial, so it's just a case of computing $E^2_{*,*}=H^*(G, H^*(X))$.
Dec 8, 2010 at 15:08 comment added Daniel Moskovich Okay... then how would the calculation go?
Dec 8, 2010 at 14:23 comment added Mark Grant I mean to reflect in an equatorial plane (in say, the first factor). Then $\{equator\}\times S^n$ is left fixed.
Dec 8, 2010 at 13:07 comment added Johannes Hahn If $\tau$ is the nontrivial group element, then $^\tau (x,x)=(x,x)$ for all $x\in S^n$ so the first action is not free. The second action is free.
Dec 8, 2010 at 12:46 comment added Daniel Moskovich How is this action not free?
Dec 8, 2010 at 9:38 history answered Mark Grant CC BY-SA 2.5