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Sergei Ivanov
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226 Answers

Votes Activity Newest
115
solving $f(f(x))=g(x)$
Mar 9 '10 at 16:48
94
Is the sphere the only surface all of whose projections are circles? Or: Can we deduce a spherical Earth by observing that its shadows on the Moon are always circular?
Sep 17 '10 at 18:40
61
Is there a dense subset of the real plane with all pairwise distances rational?
Mar 23 '10 at 22:50
61
How to solve $f(f(x)) = \cos(x)$?
Mar 9 '10 at 18:55
57
Smoothness of distance function in Riemannian Manifolds
Apr 14 '10 at 9:45
45
Is every closed set of Q² the intersection of some connected closed set of R² with Q²
Nov 16 '10 at 2:19
41
Why are free groups residually finite?
Apr 6 '10 at 9:25
38
When factors may be cancelled in homeomorphic products?
May 30 '10 at 0:30
35
Linearity of the inner product using the parallelogram law
Apr 17 '11 at 13:39
34
Smooth functions for which $f(x)$ is rational if and only if $x$ is rational
Dec 10 '10 at 14:56
33
The kissing number of a square, cube, hypercube?
Dec 31 '12 at 15:05
33
An easy proof that S(n) does not embed into A(n+1)?
May 16 '11 at 17:42
33
Does every symmetric group S_n have a single element of maximal word norm?
Dec 14 '10 at 9:43
26
Diameter of m-fold cover
Mar 3 '10 at 0:08
24
Can all convex polytopes be realized with vertices on surface of convex body?
Sep 13 '12 at 18:23
23
Zariski closed sets in C^n are of measure 0
May 21 '10 at 18:16
23
Why can't the Klein bottle embed in $\mathbb{R}^3$?
Mar 22 '10 at 12:29
22
Why is Lebesgue integration taught using positive and negative parts of functions?
May 19 '10 at 8:21
22
Microwaving Cubes
May 10 '10 at 21:20
21
Counterexample to Sard Theorem for a not-C1 map
Nov 20 '12 at 23:23
20
Is a left topological group which is a manifold a topological group?
Feb 23 '14 at 12:36
20
Convex Hull of Path Connected sets
Oct 6 '11 at 18:34
20
Set theory in practice
Mar 19 '10 at 13:25
19
square root of diffeomorphism of R: does it always exist?
Mar 23 '11 at 15:44
18
What kind of probability distribution maximizes the average distance between two points?
Dec 8 '13 at 15:32
18
Geodesics of bounded length on a Riemannian manifold
Aug 31 '11 at 16:55
18
Hausdorff dimension of the boundary of an open set in the Euclidean space - lower bound
Sep 30 '10 at 19:19
17
Are there unique geodesics in the NIL and SOL geometry?
Sep 29 '10 at 17:46
17
Do random projections (approximately) preserve convexity?
Sep 10 '12 at 16:09
17
Minimal surface which divides a convex body into two regions of equal volume
Feb 7 '11 at 13:27
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