bio | website | math.stanford.edu/~church |
---|---|---|
location | Stanford | |
age | ||
visits | member for | 5 years, 6 months |
seen | 12 hours ago | |
stats | profile views | 4,051 |
Mar 25 |
reviewed | Approve Can an abelian variety/Q have no non-trivial points over Q_sol? |
Mar 24 |
reviewed | Approve Mal'cev “rational equivalence” and model theory |
Mar 18 |
reviewed | Approve hyperbolic metrics |
Mar 15 |
answered | Does there exist a fibre bundle $K(\mathbb{Z}_4,1)\rightarrow K(\mathbb{Z}_2,1)$ with fiber $K(\mathbb{Z}_2,1)$? |
Mar 6 |
answered | Maryam Mirzakhani's works |
Mar 6 |
reviewed | Approve latex tag wiki |
Feb 26 |
comment |
$G_\mathbb{Z}$-homotopy type of rational Tits building $\Delta_{G, \mathbb{Q}}$
@J.Martel: We're considering the usual cellular homology of these buildings with integer coefficients, without interference from any groups at all. |
Feb 26 |
revised |
$G_\mathbb{Z}$-homotopy type of rational Tits building $\Delta_{G, \mathbb{Q}}$
add reference to paper arXiv:1501.01307, now that it is posted |
Feb 26 |
reviewed | Approve matrix-theory tag wiki excerpt |
Feb 24 |
awarded | Excavator |
Feb 24 |
revised |
Example of a Group which has $\text{SL}_{n}(\mathbb{Z})$ as the automorphism group
added Oliver Baues to author list (and added links to arXiv, MathReviews and journal) |
Feb 3 |
reviewed | Leave Open Is there any Lefschetz-like principle for representations of finite groups? |
Feb 3 |
reviewed | Leave Open Direct product of filters |
Feb 3 |
reviewed | Leave Open Propositional logic: Minimal set of formulas, which is consistent and complete |
Feb 3 |
reviewed | Leave Open integral or rational cohomology of real grassmannians |
Jan 28 |
comment |
Categorical proof subgroups of free groups are free?
That subalgebras of free Lie algebras over a field are free was proved by Shirshov and Witt independently, in Shirshov, Podalgebry svobodnykh lievykh algebr (Russian: Subalgebras of free Lie algebras), Mat. Sbornik N.S. 33(75) (1953), 441–452, and Witt, Die Unterringe der freien Lieschen Ringe (German: Subrings of free Lie rings), Math. Z. 64 (1956), 195–216. The same result was proved for free restricted Lie algebras in characteristic $p$ by Bryant-Kovács-Stöhr in Subalgebras of free restricted Lie algebras, Bull. Austral. Math. Soc. 72 (2005), no. 1, 147–156 (repairing earlier proofs). |
Jan 21 |
comment |
Separators in the Category of Groups
@PyRulez: a group that maps nontrivially to $\mathbb{Z}$ surjects to $\mathbb{Z}$ (take the image of a nontrivial map). |
Dec 11 |
reviewed | Reject $E_n$ structures on Symmetric Monoidal Stable infinity-categories |
Nov 19 |
answered | Breaking up the free Lie algebra into Gl irreps |
Nov 14 |
comment |
Questions about the “universal elliptic curve” over the affine $j$-line punctured at 0 and 1728
What you had was right (if $\text{SL}_2(\mathbb{Z})$ acts only on $\mathcal{H}^\circ$, it won't descend). The problem is there's no ("fine") universal elliptic curve: Let $T$ be the randomly-chosen $T=\mathbb{C}/\langle m+n(1+i)\rangle$. Let $\mathbb{Z}$ act on $T\times \mathbb{R}$ by $(t,x)\mapsto (-t,x+1)$, and set $X=(T\times\mathbb{R})/\mathbb{Z}$. This is an elliptic curve bundle over $S^1$ with every fiber $\simeq T$, but it cannot be pulled back from your $E_2$ (or any family over the $j$-line). [$X$ is nontrivial because e.g. $H_1(X)=\mathbb{Z}\neq \mathbb{Z}^3=H_1(T\times S^1)$.] |