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age 25
visits member for 4 years, 2 months
seen 19 hours ago

Feb
18
reviewed Reject Differentiable function on bad sets.
Feb
10
reviewed Approve Evaluating $\int\frac{3x+1}{2x^2-2x+3}dx$
Feb
8
reviewed Approve At least one prime between N and N-(sqrtN)
Feb
7
comment The groups $[\Sigma^nX,Y]$ versus the homotopy groups
@nik: I understand what you're saying now. But the questions are the end are to be taken to mean: "in these circumstances, does the knowledge of these groups for all $X$ give us information?" (the questions you linked being taking $X=S^0$)
Feb
7
comment The groups $[\Sigma^nX,Y]$ versus the homotopy groups
@nik: as interesting as those questions may be, I don't see any reference to the groups I allude to in this one.
Feb
7
comment The groups $[\Sigma^nX,Y]$ versus the homotopy groups
@ZhenLin: yes, but of a different space! In any case, thanks, that's a nice observation.
Feb
7
asked The groups $[\Sigma^nX,Y]$ versus the homotopy groups
Jan
31
asked Homology with local coefficients in a $\mathbb{Z}[\pi_1(X)]$-module
Jan
27
comment Does there exist a surface homemomorphic to a torus with positive Gaussian curvature?
@Felipe: any compact surface in $\mathbb{R}^3$ has a point with positive curvature. Indeed, it is bounded, thus it lies inside of a big enough sphere. Now reduce the sphere's radio until it first touches the surface in a point. That point of the surface must therefore have positive curvature. (You should fill in the details for this argument).
Jan
27
comment Does there exist a surface homemomorphic to a torus with positive Gaussian curvature?
@Felipe: no (deform a little bit the tip of a sphere for example), but the Euler characteristic is. Therein lies the power of Gauss-Bonnet! It combines topological data (Euler characteristic) with geometrical data (global curvature).
Jan
26
comment How to introduce category theory to a high school audience?
I agree with what Martin said. The first examples that come to mind are lcm/gcd of integers and sup/inf of real numbers. There are many other elementary examples like these.
Jan
23
revised Verification of my solution of $xy'=2y$
changed undescriptive title
Jan
18
awarded  Nice Question
Jan
18
reviewed Approve magical isoceles triangle and 13/15 ratio
Jan
18
reviewed Approve Show a module is simple
Jan
9
comment Stopping the “Will I need this for the test” question
This is as depressing as it is true.
Dec
30
revised When are generalized Severi-Brauer varieties trivial?
I mistook dimension for -reduced dimension-. Also, added link to the MO counterpart
Dec
28
reviewed Reject Solving $\phi(n)=22$
Dec
27
reviewed Edit What is the benefit of the theory of categories?
Dec
27
revised What is the benefit of the theory of categories?
edited some typos