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awarded  Popular Question
Aug
13
comment Equivalence of Definitions of Principal $G$-bundle
There is another one: a principal $G$-bundle is a fiber bundle with fiber $G$ and structure group $G$ where $G$ acts on itself by left translations. This is the definition of Davis & Kirk.
Jul
18
awarded  Popular Question
Jun
23
comment Any compact embedded $2$-dimensional hypersurface in $\mathbb R^3$ has a point of positive Gaussian curvature
@Dtseng: true, thank you. I've corrected it. Some months after I wrote this answer I wrote it up in all formality here (in Spanish).
Jun
23
revised Any compact embedded $2$-dimensional hypersurface in $\mathbb R^3$ has a point of positive Gaussian curvature
added 36 characters in body
Jun
13
awarded  Revival
Jun
7
comment Homology of a co-h-space manifold
Corollary 13.66 in Switzer's book proves that for any cohomology theory with products, the product is trivial on a suspension. Maybe you can generalize his proof to co-h-spaces.
Jun
3
comment Characterizations of the $p$-Prüfer group
More than four years later, I should edit that seventh item to change those inclusions to "multiply by $p$" maps, but I don't want to bump the question to the front page.
Jun
3
comment Clarify: “$S^0$, $S^1$ and $S^3$ are the only spheres which are also groups”
The point is that the operation gotten from such a set-theoretical bijection has no reason to respect the topological/differentiable structure of $S^k$ in any way. So what they mean is, a group structure in $S^k$ that behaves well with respect to the topology/geometry. (Hence the Lie groups appearing in the answer below).
Jun
2
awarded  Revival
May
29
comment Why is the cartesian product so categorically robust?
This reminds me of this answer: math.stackexchange.com/a/25460/2614
May
29
comment Is there an analogue of Eilenberg-Maclane spaces for homology?
This is essentially this MO question: mathoverflow.net/questions/1438/… , and Mike's accurate answer & comment are essentially Tyler's.
May
27
awarded  Notable Question
May
19
asked Spectral sequence for computing the homotopy fixed points in unstable equivariant homotopy theory
May
15
comment References for equivariant cohomology
You could start with the "What is... equivariant cohomology?" article from the Notices of the AMS. Then I heard there is a book by Bredon on the subject.
May
13
awarded  Nice Answer
May
1
comment Curious remark of D. Ravenel
This article is incredibly funny.
Apr
30
comment If there are injective homomorphisms between two groups in both directions, are they isomorphic?
See also mathoverflow.net/questions/1058/when-does-cantor-bernstein-hold
Apr
16
comment What are some beautiful examples of adjunctions?
math.stackexchange.com/questions/46708/…
Apr
9
revised Computation of $Ext^*_R(k,k)$ as an algebra using a dga-resolution
edited tags