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Feb
9 |
accepted | What's in the genus of the cubic lattice? |
Feb
9 |
comment |
What's in the genus of the cubic lattice?
I think I didn't put it together until now, that odd unimodular lattices make a genus, and that's the genus containing $\mathbf{Z}^n$. |
Feb
4 |
comment |
What's in the genus of the cubic lattice?
Thanks, Noam. - |
Feb
4 |
comment |
What's in the genus of the cubic lattice?
Thanks for the O'Meara reference. The last footnote on the last page, referring to that Kneser work, is: "See M. Kneser (1957). For an example of the classical approach using 'reduction theory' we refer to BW Jones (1950)." I'd be interested to find out what O'M means, but I didn't find the Jones book yet. |
Feb
3 |
comment |
What's in the genus of the cubic lattice?
Thanks Jeremy. How does magma do it? And is it the kind of thing that was known, or could have been, to Zolotareff? |
Feb
3 |
asked | What's in the genus of the cubic lattice? |
Jan
31 |
revised |
Is there an approach to Gabber's theorem from the singular support of coherent sheaves?
"I heard" from somebody specific |
Jan
30 |
awarded | Nice Question |
Jan
30 |
revised |
Is there an approach to Gabber's theorem from the singular support of coherent sheaves?
I had "LE = E x BE" which is not quite right. |
Jan
30 |
comment |
Is there an approach to Gabber's theorem from the singular support of coherent sheaves?
Hi Pavel. I think I am exactly asking why the equivariance implies Gabber's theorem. It doesn't seem like you get it from just any kind of circle action. Is it a special case of a theorem about coherent sheaves on a more general class of derived stacks? |
Jan
28 |
asked | Is there an approach to Gabber's theorem from the singular support of coherent sheaves? |
Dec
19 |
comment |
elliptic curves and group cohomology
When $R = \mathbf{C}$, a line bundle on $M_G$ gives for each pair of commuting elements $(x,y)$ in $G$ a homomorphism $\rho:Z_G(x,y) \to \mathbf{C}^*$. If I represent $k$ as a $\mathbf{C}^*$-valued $3$-cocycle $k(g_1,g_2,g_3)$, is there an explicit formula for $\rho(g)$ in terms $k$? Perhaps $\rho(g) = k(x,y,g)$? |
Oct
23 |
awarded | Yearling |
Jul
23 |
comment |
highest weight the half-sum of positive roots
Is it the observation attributed to Kostant in the first two paragraphs here? mathoverflow.net/questions/14770/… |
Jun
28 |
comment |
What is deforming this non-complete intersection like?
Thanks Will and Jason. Jason, can a non-CM ideal be flatly deformed to a CM ideal? Or are you telling me that this variety has no smooth deformations at all! |
Jun
28 |
revised |
What is deforming this non-complete intersection like?
wrong equations |
Jun
28 |
asked | What is deforming this non-complete intersection like? |
Mar
29 |
comment |
Has any attempt been made to classify finite groupoids?
Extensions of $G$ by a nonabelian $M$ are classified by cohomology of $G$ with coefficients in what the ancients called a crossed module; i.e. by homotopy classes of maps from $BG$ to the delooping of $\mathrm{Aut}(BM)$. Since $M_{12}$ has no center, $\mathrm{Aut}(BM_{12}) \cong \mathrm{Out}(BM_{12}) \cong \mathbf{Z}/2$. That means there can be no nontrivial extensions of a group like $\mathrm{SL}_3(\mathbf{F}_3)$ or $\mathrm{PGL}_3(\mathbf{F}_3)$ by $M_{12}$, right? |
Mar
17 |
comment |
Does a polytope have a self-indexing shelling?
Thanks Richard, I hadn't seen this question. Besides not allowing deformations, another difference is that I am curious about shellings that do not come from linear functions. |
Mar
17 |
asked | Does a polytope have a self-indexing shelling? |