bio  website  mate.dm.uba.ar/~aldoc9 

location  Buenos Aires  
age  40  
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 prooftree 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 wellknown 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 AmitsurLevitzki identity essentially unique?
Your last paragraph can be expressed succintly using the notion of Tideals. 
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? 