Mariano Suárez-Alvarez
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Apr
24
comment How to check that an ideal of $\mathbb{C}[GL_n]$ is a coideal or not?
Are those generators something?
Apr
22
comment Using TikZ in papers
@ScottMorrison, sadly, it is till stuck in the same versions of everything as when you wrote that comment! Today I spend a couple of hours trying to get a file to compile correctly on arXiv :-(
Apr
12
comment Are there non-smoothable homotopy/homology spheres?
What does "topologically standard" mean?
Apr
11
comment Unclear asymmetry in Lie-algebra module structure on space of linear transformations Hom(V,W)
That sentence in the comment sheds more light on the matter than 1729 mentions of the word groupoid :-)
Apr
11
comment Unclear asymmetry in Lie-algebra module structure on space of linear transformations Hom(V,W)
How much obscure is your second paragraph compared to the first one!
Apr
3
awarded  Nice Answer
Mar
31
comment Existence of a particular kind of polygonal subdivisions of surfaces
How does one pass from tilings on the hyperbolic plane to subdivision if surfaces? In particular: which of those tilings descend to what finite tilings of which surfaces?
Mar
13
comment Examples of unexpected mathematical images
It is better to link to arxiv abstract pages and not the PDF directly
Mar
12
comment Algebraic curves that enclose and exclude given points in the plane
Draw a curve which does what you want and approximate it by an algebraic one: mathoverflow.net/questions/104609/algebraic-curve-approximation
Mar
5
comment Can we count the number of simple modules for a reduced enveloping algebra?
It is always a pleasure to read your answers, Jim!
Mar
5
comment Automorphisms of Cartesian products
You can act with different automorphism if X on each coordinate of X^r, and that is not in your subgroup.
Mar
5
awarded  Nice Answer
Feb
27
comment What part is left unsolved in the Unknotting problem? (after results of Bar-Natan, Khovanov, Kronheimer and Mrowka)
$O(\sqrt{\text{crossings}})$ does not give time enough to even look at all the crossings.
Feb
27
comment A cohomology class associated with a complex representation of a group
(Here LBG is the free loop space on BG) The first Chern class of this descended bundle is an element of $H^2(LBG,\mathbb Z)$, which is a direct sum of cohomologies of centralizers. Is that class the same as the one described? That would be an answer to "what is c(V)?".
Feb
27
comment A cohomology class associated with a complex representation of a group
@Andreas, well, I know that the class is a bunch of homomorphisms (which are coherent in some way): that is how it is defined! What I am asking is what the class is, in the sense of is it something? For example, from V you can construct a vector bundle $\tilde V=EG\times_GV$ on $BG$, which you can pull back along the evaluation map $LBG\times S^1\to BG$ to get a vector bundle on that product which descends onto $LBG\times_{S^1}S^1$, which is $LBG$.
Feb
26
comment Dimension of the space of Jacobi fields along $\gamma$ vanishing at $p$ and $q$ is even?
Is there any intuition of why this should be true?
Feb
25
comment A cohomology class associated with a complex representation of a group
I honestly do not understand what «that is all» means in this context.
Feb
25
revised A cohomology class associated with a complex representation of a group
added 76 characters in body
Feb
25
revised A cohomology class associated with a complex representation of a group
added 516 characters in body
Feb
25
comment A cohomology class associated with a complex representation of a group
@EhudMeir, indeed, my example with the determinant was an example of something else! :-| I'll correct it. if I start with with a $2$-cocycle $\alpha:G\times G\to\CC^\times$, fix $g\in G$ and let $\beta:h\in G_g\mapsto \alpha(g,h)/\alpha(h,g)\in\CC^\times$, I am only being able to prove that $d\beta=\beta^2\smile\beta^2$, no that it is a $1$-cocycle on $G_g$; is that construction treated somewhere? (I can do it if $\alpha:G\times G^{\ad}\to\CC^\times$ is a $1$-cocycle giving an element of $\Ext^1(\ZZ G^\ad,\CC^\times)$, though: is that what you meant?)