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location Moscow, Russia
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visits member for 4 years, 1 month
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umagon at google mail


Jul
17
reviewed Close Prove that the cyclic group of order $3$ is isomorphic to $\Bbb Z_3$ under addition. Show answer using a proof and justification for each step.
Jul
17
reviewed Close Permutation problem - How many permutations are there such that no two numbers are immediately adjecent?
Jul
17
reviewed No Action Needed A maximal subset of $S^2$ with respect to a connectedness property
Jul
17
reviewed Leave Closed I want to study Numerical linear algebra
Jul
16
reviewed Reject suggested edit on Dilation and translation of the Dirac Delta distribution
Jul
16
reviewed Close How to put these equations in standard form
Jul
16
reviewed No Action Needed Finitely Generated Subset
Jul
16
reviewed Close Wolfram Alpha “Rule of Three”
Jul
16
reviewed Close Give an example of a function $f$ satisfying $\lim_{x\to 0}(f(x)f(2x))=0$,but $\lim_{x\to 0}f(x)$ does not exists
Jul
16
reviewed No Action Needed How many positive integer solutions are there to the inequality $x_1+x_2+…+x_r\le n$?
Jul
16
reviewed Leave Closed Area Under Curve and Differential Equations
Jul
15
reviewed No Action Needed Correlated Rayleigh random variable generation
Jul
15
reviewed Looks OK Logarithmic equations with different bases
Jul
15
reviewed Reviewed Trailing zeroes on factorial?
Jul
15
reviewed No Action Needed “All vertices of a convex pentagon are lattice points, and its sides have integral length. Show that its perimeter is even.”
Jul
15
comment Sum involving binomial coefficients
Well, have you tried guessing general answer from first few values?
Jul
15
reviewed Looks OK Very simple proof help about integers
Jul
15
comment How to compute homotopy classes of maps on the 2-torus?
(I wish I knew a reference where all this is explained more clearly...)
Jul
15
comment How to compute homotopy classes of maps on the 2-torus?
@Qiaochu ...i.e. $\pi_2(X)/\langle t-t^a,t-t^b\mid t\in\pi_2\rangle$ is actually $H^2(\mathbb T^2;\pi_2(X))$, where $\pi_2(X)$ is the local system s.t. generators of $\pi_1(\mathbb T)$ act as $t\mapsto t^a$ and $t\mapsto t^b$.
Jul
15
comment How to compute homotopy classes of maps on the 2-torus?
@Qiaochu The answer for $D^2$ is different because the coboundary map is different. For $[S,X]$ (and let's consider the case $\pi_1(X)=0$ for simplicity) we're talking about $H^2(S;\pi_2(X))$.