bio  website  math.berkeley.edu/~ianagol 

location  Berkeley  
age  44  
visits  member for  5 years, 1 month 
seen  1 hour ago  
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I'm a professor at UC Berkeley working predominantly in the field of lowdimensional topology.
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Is there a “good” reason that the universal central extension of $SL(2,\mathbb Z)$ is $Br_3$?
added 70 characters in body 
1h

answered  Is there a “good” reason that the universal central extension of $SL(2,\mathbb Z)$ is $Br_3$? 
Dec 10 
awarded  Good Answer 
Dec 10 
comment 
Fundamental groups and homology groups of closed subsets of the plane
See this question: mathoverflow.net/q/189323/1345 
Dec 10 
awarded  Nice Answer 
Dec 9 
answered  Can a subset of the plane have nontrivial $H_2$ or $\pi_2$? 
Dec 8 
awarded  Good Answer 
Nov 23 
answered  Koebe–Andreev–Thurston theorem  where can I find a proof? 
Nov 18 
comment 
amenable + without $BS(m,n)$+finite $K(G,1)$implies virtually cyclic?
Note for a finite dim. $K(G,1)$, virtually cyclic is equivalent to infinite cyclic (or trivial I suppose), since there can be no torsion. 
Nov 5 
comment 
Which mapping class group representations come from algebraic geometry?
It would be interesting if you could flesh out the details of this approach. 
Nov 3 
comment 
Classification of elements in mapping class groups
see also flipper by Mark Bell: front.math.ucdavis.edu/1410.1358 bitbucket.org/Mark_Bell/flipper 
Nov 2 
awarded  Necromancer 
Oct 31 
awarded  Yearling 
Oct 27 
comment 
Can infinitely many alternating knots have the same Alexander polynomial?
No Ryan, KinoshitaTerasaka is not alternating. 
Oct 21 
comment 
Why is it so hard to compute $\pi_n(S^n)$?
I'm at a loss as to what sort of answer you're looking for, but it is funny to contemplate what $\pi_n(S^n)$ would look like if it weren't $\mathbb{Z}$. There is a ring structure coming from composition of maps, which would make $\pi_n(X)$ into a module over this ring for any $X$. But if this ring is not $\mathbb{Z}$, it's hard to envision how one may use this to arrive at a contradiction. 
Oct 16 
answered  Gauss Codes that produce classical knots as opposed to virtual knots 
Oct 15 
comment 
discrete group cohomology vs continuous group cohomology for profinite groups
Ok, I guess I had in mind the profinite completion of a finitely generated group, but clearly $G^\delta$ will be infinitely generated if infinite. There are now many finitely generated "good" groups $G$ known, but I don't know whether this implies $\hat{G}^\delta$ is good? 
Oct 14 
comment 
discrete group cohomology vs continuous group cohomology for profinite groups
Not sure I understand why this is equivalent to goodness: I thought that was an isomorphism between the cohomology of a group with finite module coefficients and its profinite completion. 
Oct 12 
comment 
discrete group cohomology vs continuous group cohomology for profinite groups
This should be true for $H^1$ and $G$ finitely generated by a result of Nikolov and Segal that finiteindex subgroups are open. 
Oct 11 
comment 
MilnorWolf result on growth of solvable groups
Certain special classes of solvable groups are covered by the simple argument in the appendix to Gromov's paper on groups of polynomial growth by Tits. For example, the argument applies to a lattice in a 3dimensional solvable Lie group. The point is that a finitely generated abelianbycyclic group has exponential growth if the cyclic group acts on the abelian subgroup with an eigenvalue $>1$ in absolute value. Maybe one can show that a nonvn solvable group contains such a subgroup or else contains a solvable BaumslagSolitar subgroup? 