152,814 reputation
15329601
bio website math.berkeley.edu/~qchu
location Berkeley, CA
age 24
visits member for 4 years, 3 months
seen 2 hours ago

I'm a third-year graduate student in pure mathematics at UC Berkeley. You can contact me at qchu[at]math[dot]berkeley[dot]edu.


22h
answered Every vector bundle over $[0,1]^n$ is trivial
23h
revised Examples of types of mathematical models
edited tags
23h
revised Not all finitely-presented groups are fundamental groups of closed 3-manifolds
added 220 characters in body
23h
answered Not all finitely-presented groups are fundamental groups of closed 3-manifolds
1d
comment Rational function interpolation?
If you know bounds $\deg p, \deg q$ on the degrees of the numerator and denominator then it takes $\deg p + \deg q + 1$ points.
1d
comment Is this simple drawing a category?
I admit my motivations are selfish: I don't want the list of questions I've recently answered to be cluttered by low-vote answers where I just say "yes" or whatever.
1d
comment The generator of compact cohomology of punctured plane
Compactly supported cohomology is not invariant under non-proper homotopies, so your argument doesn't work.
1d
comment What happens when you drop “étale” from the construction of étale fundamental groups
Suppose $X = \text{Spec } k$. Then the category of finite morphisms to $X$ is the category of finite-dimensional commutative $k$-algebras. This seems to me like a pretty complicated category even when $k$ is algebraically closed, and in particular should be very far from being the kind of category one can run Grothendieck's Galois theory on.
1d
comment What type of expression is this: (X/Y)*X
It's a rational function of two variables.
1d
answered What does “minus the zero section” mean?
2d
comment Is this simple drawing a category?
Yes. The way you've drawn $f$ and $g$ they can't be composed, so there's no further data to specify.
Oct
22
answered Non-Galois number fields and complex embeddings
Oct
22
answered Does the functor that preserves limit always have a left adjoint?
Oct
20
awarded  Nice Answer
Oct
20
awarded  ring-theory
Oct
19
comment Why only two binary operations?
@isomorphismes: well, who knows? We could spend all day arguing about precisely what is and is not natural. What I'm willing to say is that categories have been a very fruitful point of view historically and I expect they'll continue to be in the future.
Oct
19
revised Why only two binary operations?
added 109 characters in body
Oct
19
answered Why only two binary operations?
Oct
19
comment Compactness of Lie groups
@Brenin: I mean two things by this, which is why I didn't want to be precise. First, $\text{GL}_n(\mathbb{C})$ deformation retracts onto $\text{U}(n)$, so the two are homotopy equivalent. But second, it turns out that the two have essentially the same representation theory, provided that you're careful to restrict your attention to algebraic representations of $\text{GL}_n(\mathbb{C})$.
Oct
19
answered automorphism of the projective space $\mathbb{P}_A^n$