bio  website  math.berkeley.edu/~qchu 

location  Berkeley, CA  
age  24  
visits  member for  5 years, 3 months 
seen  30 mins ago  
stats  profile views  57,110 
I am a thirdyear graduate student at UC Berkeley. I'm interested in the interplay between homotopy theory, quantum field theory, manifold topology, and higher category theory.
1h

asked  Twisted equivariant modular forms? 
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revised 
How many geometric structures on manifolds are there?
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2h

answered  How many geometric structures on manifolds are there? 
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Categorical proof subgroups of free groups are free?
@Todd: Oh, so a number theorist! 
20h

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Does this symmetrization operator have a name? Any theory?
It's averaging over an action of a particular finite group, namely $\mathbb{Z}_2^n$. I think in some contexts the more general operation of averaging over an action of a finite group is called the Reynolds operator. 
1d

awarded  Nice Answer 
1d

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What is the original reference for disorientations on tangle diagrams?
Can you describe disoriented tangles by some universal property? 
1d

revised 
Categorical proof subgroups of free groups are free?
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revised 
Categorical proof subgroups of free groups are free?
added 39 characters in body 
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comment 
Categorical proof subgroups of free groups are free?
@HJRW: thanks for the warning. I picked that notation because I halfremembered that similar property, but it seems I remembered it wrong. I'll pick something else. 
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revised 
Categorical proof subgroups of free groups are free?
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answered  Categorical proof subgroups of free groups are free? 
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Example of torsion in orientable manifolds?
I think this example would be more recognizable as $\mathbb{RP}^3$. 
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Bar Construction Model of Ring Spectrum Quotient
Re: the last sentence, take $G$ discrete and work in an ordinary category. An action of $G$ on an object in a category $C$ is precisely a diagram $BG \to C$ and the categorical quotient of that object by that action is precisely the colimit of this diagram in $C$. The ABGHR definition is a natural generalization of this. 
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Categorical proof subgroups of free groups are free?
Prospects for a categorical proof seem poor in that subgroups of free groups are not canonically free. I think freeness is in some sense a red herring and one should look for some other grouptheoretic property equivalent to freeness but which makes no reference to a choice of free generators. Maybe cohomological dimension $1$? 
Jan 24 
awarded  Nice Answer 
Jan 23 
revised 
Examples of categorical adjunctions in analysis, Lie theory, and differential geometry?
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Jan 23 
answered  Examples of categorical adjunctions in analysis, Lie theory, and differential geometry? 
Jan 22 
awarded  Enlightened 
Jan 22 
awarded  Nice Answer 