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visits member for 5 years, 3 months
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2d
comment How many geometric structures on manifolds are there?
You should probably make explicit what makes your question different from «what are the coverings of linear Lie groups?» which is what the comments are converging to.
2d
comment Linearization of line bundle
An example would be additive group $G_{ad}$ acting by translations on the fibers of $X\times k\to X$ and trivially on $X$.
Jan
28
comment Categorical proof subgroups of free groups are free?
The same is true of free Lie algebras: they are those of global dimension 1.
Jan
23
comment Proofs without words
If you cannot tell the difference between a proof-tree and a proof without words in the tradition of, say, the AMM Monthly, then that is clearly a limitation of yours. I would rather you start a meta thread, or a blog, instead of further polluting this thread with what is clearly rather orthogonal chatter.
Jan
23
comment Proofs without words
@goblin, I am afraid that you have completely misunderstood the concept. The idea is pictures which have the rather amazing capability of immediately suggesting on the mind of the viewer the idea of a proof. How on earth you managed to get from the rather well-known idea involved in this question to «proofs without logic» is a mystery to me.
Jan
9
awarded  Nice Answer
Dec
30
comment Localizations or quotients of categories?
@FilippoAlbertoEdoardo, consider an antisimmetric category (so that for distinct objects $x$ and $y$ at most one of the sets $\hom(x,y)$ and $\hom(y,x)$ is nonempty,and there are no nonidentity endomorphisms) and consider the equivalence relation which identifies all elements in each nonempty $\hom$ set. This is not a lozalization, because there are no isomrphisms in the resulting category.
Dec
16
comment Defining the cup product in Ext using a Kunneth formula
The cup product is just the composition of maps in the derived category. If you want to actually compute, that's not very helpful, though.
Dec
13
awarded  Nice Answer
Dec
12
awarded  Great Answer
Dec
12
awarded  Popular Question
Dec
11
comment The Euler characteristic of Hilbert series
Knot theory people use «graded Euler characteristic» if I recall correctly, but it seems restricted to that crowd.
Dec
11
asked The Euler characteristic of Hilbert series
Dec
6
comment Higher Homotopy Groups
That we do have a map follows from the celebrated Theorem on The Existence Of Constant Maps.
Nov
22
comment Is the Amitsur-Levitzki identity essentially unique?
Your last paragraph can be expressed succintly using the notion of T-ideals.
Nov
21
comment Rigid nilpotent Lie algebras
The condition by Carles is on any lie algebra or on nilpotent ones?
Nov
18
revised Is there a natural way to view the proof of Hilbert 90?
added 71 characters in body
Nov
18
comment Cohomology of SL(2,R) with coefficients given by linear action
You are looking at $SL_2(\mathbb R)$ as a discrete group?
Nov
17
revised Is there a natural way to view the proof of Hilbert 90?
added 78 characters in body
Nov
17
answered Is there a natural way to view the proof of Hilbert 90?