bio | website | math.stanford.edu/~church |
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location | Stanford | |
age | ||
visits | member for | 5 years, 3 months |
seen | 7 hours ago | |
stats | profile views | 3,834 |
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. $H_1(X)=\mathbb{Z}\neq \mathbb{Z}^3=H_1(T\times S^1)$.] |
Nov 14 |
comment |
Questions about the “universal elliptic curve” over the affine $j$-line punctured at 0 and 1728
It looks to me like $E_2$ is a $\mathbb{P}^1$-bundle over $\text{SL}_2(\mathbb{Z})\backslash \mathcal{H}^\circ$; for $\gamma=-\text{Id}$ you have $\gamma\cdot(z,\tau)=(-z,\tau)$, so the fiber over $\tau\in \text{SL}_2(\mathbb{Z})\backslash \mathcal{H}^\circ$ is $E_\tau/\langle\pm 1\rangle\simeq \mathbb{P}^1$. (This commment may not make sense in the future if the question is revised.) |
Nov 9 |
awarded | Custodian |
Nov 9 |
reviewed | Reviewed CD - continuous development |
Nov 9 |
awarded | Custodian |
Nov 9 |
reviewed | Approve Questions related to a previous question about interpolation based on non-decreasing polynomials |
Oct 12 |
awarded | Yearling |
Aug 30 |
comment |
Corvallis 1979 proceedings
The AMS pages for these books are now ams.org/books/pspum/033.1 and ams.org/books/pspum/033.2; however they no longer seem to be freely available. |
Jun 26 |
reviewed | Reject nontrivial theorems with trivial proofs |
Jun 17 |
reviewed | Reject nontrivial theorems with trivial proofs |
Jun 15 |
revised |
$G_\mathbb{Z}$-homotopy type of rational Tits building $\Delta_{G, \mathbb{Q}}$
clarify result for orbits of chains, add remark on PID |
Jun 15 |
revised |
$G_\mathbb{Z}$-homotopy type of rational Tits building $\Delta_{G, \mathbb{Q}}$
correct ell = |K_0| to ell = |K_0| - 1 |
Jun 15 |
answered | $G_\mathbb{Z}$-homotopy type of rational Tits building $\Delta_{G, \mathbb{Q}}$ |
Jun 8 |
comment |
Integral of sin(x)/sqrt(x) from 0 to \pi
@NoamD.Elkies I agree that the downvotes may have been hasty; I didn't downvote, but I easily could have. However questions like this about evaluating definite integrals seem to be more at home at math.SE (even quite difficult integrals, which often receive extremely impressive answers there!). So the best outcome may be for this question to be moved to math.SE. |
Jun 4 |
awarded | Custodian |
Jun 4 |
reviewed | Reject nontrivial theorems with trivial proofs |
Jun 4 |
reviewed | Reject nontrivial theorems with trivial proofs |