User Sergei Ivanov

122 votes

Accepted

solving $f(f(x))=g(x)$

answered Mar 9, 2010 at 16:48

104 votes

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Is the sphere the only surface with circular projections? Or: Can we deduce a spherical Earth by observing that its shadows on the Moon are circular?

answered Sep 17, 2010 at 18:40

69 votes

How to solve $f(f(x)) = \cos(x)$?

answered Mar 9, 2010 at 18:55

65 votes

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Is there a dense subset of the real plane with all pairwise distances rational?

answered Mar 23, 2010 at 22:50

65 votes

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Smoothness of distance function in Riemannian Manifolds

answered Apr 14, 2010 at 9:45

45 votes

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Is every closed set of Q² the intersection of some connected closed set of R² with Q²

answered Nov 16, 2010 at 2:19

44 votes

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Why are free groups residually finite?

answered Apr 6, 2010 at 9:25

40 votes

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When factors may be cancelled in homeomorphic products?

answered May 30, 2010 at 0:30

40 votes

Linearity of the inner product using the parallelogram law

answered Apr 17, 2011 at 13:39

39 votes

An easy proof that $S(n)$ does not embed into $A(n+1)$?

answered May 16, 2011 at 17:42

36 votes

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Smooth functions for which $f(x)$ is rational if and only if $x$ is rational

answered Dec 10, 2010 at 14:56

33 votes

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Does every symmetric group S_n have a single element of maximal word norm?

answered Dec 14, 2010 at 9:43

33 votes

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The kissing number of a square, cube, hypercube?

answered Dec 31, 2012 at 15:05

30 votes

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Zariski closed sets in C^n are of measure 0

answered May 21, 2010 at 18:16

29 votes

Why is Lebesgue integration taught using positive and negative parts of functions?

answered May 19, 2010 at 8:21

29 votes

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Counterexample to Sard's theorem for a non-C1 map

answered Nov 20, 2012 at 23:23

26 votes

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Diameter of m-fold cover

answered Mar 3, 2010 at 0:08

25 votes

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Why can't the Klein bottle embed in $\mathbb{R}^3$?

answered Mar 22, 2010 at 12:29

25 votes

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Can all convex polytopes be realized with vertices on surface of convex body?

answered Sep 13, 2012 at 18:23

23 votes

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Microwaving Cubes

answered May 10, 2010 at 21:20

23 votes

Hausdorff dimension of the boundary of an open set in the Euclidean space - lower bound

answered Sep 30, 2010 at 19:19

22 votes

Set theory in practice

answered Mar 19, 2010 at 13:25

21 votes

Convex Hull of Path Connected sets

answered Oct 6, 2011 at 18:34

21 votes

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Double a manifold with boundary

answered Sep 25, 2012 at 10:22

20 votes

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Is a left topological group which is a manifold a topological group?

answered Feb 23, 2014 at 12:36

20 votes

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To what extent is convexity a local property?

answered Apr 21, 2010 at 18:25

19 votes

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Geodesics of bounded length on a Riemannian manifold

answered Aug 31, 2011 at 16:55

19 votes

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Minimal surface which divides a convex body into two regions of equal volume

answered Feb 7, 2011 at 13:27

19 votes

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square root of diffeomorphism of R: does it always exist?

answered Mar 23, 2011 at 15:44

19 votes

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What kind of probability distribution maximizes the average distance between two points?

answered Dec 8, 2013 at 15:32

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227 Answers

solving $f(f(x))=g(x)$

Is the sphere the only surface with circular projections? Or: Can we deduce a spherical Earth by observing that its shadows on the Moon are circular?

How to solve $f(f(x)) = \cos(x)$?

Is there a dense subset of the real plane with all pairwise distances rational?

Smoothness of distance function in Riemannian Manifolds

Is every closed set of Q² the intersection of some connected closed set of R² with Q²

Why are free groups residually finite?

When factors may be cancelled in homeomorphic products?

Linearity of the inner product using the parallelogram law

An easy proof that $S(n)$ does not embed into $A(n+1)$?

Smooth functions for which $f(x)$ is rational if and only if $x$ is rational

Does every symmetric group S_n have a single element of maximal word norm?

The kissing number of a square, cube, hypercube?

Zariski closed sets in C^n are of measure 0

Why is Lebesgue integration taught using positive and negative parts of functions?

Counterexample to Sard's theorem for a non-C1 map

Diameter of m-fold cover

Why can't the Klein bottle embed in $\mathbb{R}^3$?

Can all convex polytopes be realized with vertices on surface of convex body?

Microwaving Cubes

Hausdorff dimension of the boundary of an open set in the Euclidean space - lower bound

Set theory in practice

Convex Hull of Path Connected sets

Double a manifold with boundary

Is a left topological group which is a manifold a topological group?

To what extent is convexity a local property?

Geodesics of bounded length on a Riemannian manifold

Minimal surface which divides a convex body into two regions of equal volume

square root of diffeomorphism of R: does it always exist?

What kind of probability distribution maximizes the average distance between two points?