User Sergei Ivanov

119 votes

Accepted

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

answered Mar 9, 2010 at 16:48

102 votes

Accepted

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?

mg.metric-geometry

answered Sep 17, 2010 at 18:40

67 votes

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

ca.classical-analysis-and-odes fractional-iteration

answered Mar 9, 2010 at 18:55

62 votes

Accepted

Smoothness of distance function in Riemannian Manifolds

dg.differential-geometry

answered Apr 14, 2010 at 9:45

61 votes

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

mg.metric-geometry discrete-geometry

answered Mar 23, 2010 at 22:50

45 votes

Accepted

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

gn.general-topology

answered Nov 16, 2010 at 2:19

41 votes

Accepted

Why are free groups residually finite?

gr.group-theory topological-groups profinite-groups

answered Apr 6, 2010 at 9:25

40 votes

Accepted

When factors may be cancelled in homeomorphic products?

gn.general-topology

answered May 30, 2010 at 0:30

37 votes

Linearity of the inner product using the parallelogram law

linear-algebra norms inner-product

answered Apr 17, 2011 at 13:39

37 votes

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

gr.group-theory permutation-groups

answered May 16, 2011 at 17:42

35 votes

Accepted

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

nt.number-theory real-analysis

answered Dec 10, 2010 at 14:56

33 votes

Accepted

The kissing number of a square, cube, hypercube?

mg.metric-geometry discrete-geometry packing-and-covering sphere-packing

answered Dec 31, 2012 at 15:05

33 votes

Accepted

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

gr.group-theory

answered Dec 14, 2010 at 9:43

26 votes

Accepted

Diameter of m-fold cover

mg.metric-geometry

answered Mar 3, 2010 at 0:08

26 votes

Accepted

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

ca.classical-analysis-and-odes dg.differential-geometry

answered Nov 20, 2012 at 23:23

25 votes

Accepted

Zariski closed sets in C^n are of measure 0

measure-theory

answered May 21, 2010 at 18:16

24 votes

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

real-analysis integration measure-theory

answered May 19, 2010 at 8:21

24 votes

Accepted

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

at.algebraic-topology reference-request

answered Mar 22, 2010 at 12:29

24 votes

Accepted

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

mg.metric-geometry co.combinatorics geometry convex-polytopes

answered Sep 13, 2012 at 18:23

23 votes

Accepted

Microwaving Cubes

ca.classical-analysis-and-odes

answered May 10, 2010 at 21:20

22 votes

Set theory in practice

set-theory

answered Mar 19, 2010 at 13:25

21 votes

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

gn.general-topology

answered Sep 30, 2010 at 19:19

21 votes

Convex Hull of Path Connected sets

gt.geometric-topology convex-hulls

answered Oct 6, 2011 at 18:34

20 votes

Accepted

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

gr.group-theory gn.general-topology topological-groups

answered Feb 23, 2014 at 12:36

19 votes

Accepted

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

pr.probability mg.metric-geometry

answered Dec 8, 2013 at 15:32

19 votes

Accepted

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

mg.metric-geometry calculus-of-variations classical-mechanics geometric-measure-theory

answered Feb 7, 2011 at 13:27

19 votes

Accepted

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

dg.differential-geometry ds.dynamical-systems

answered Mar 23, 2011 at 15:44

18 votes

Accepted

Geodesics of bounded length on a Riemannian manifold

riemannian-geometry

answered Aug 31, 2011 at 16:55

18 votes

Accepted

To what extent is convexity a local property?

fa.functional-analysis gt.geometric-topology mg.metric-geometry co.combinatorics

answered Apr 21, 2010 at 18:25

17 votes

Accepted

Are there unique geodesics in the NIL and SOL geometry?

gt.geometric-topology dg.differential-geometry

answered Sep 29, 2010 at 17:46

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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 $f(f(x)) = \cos(x)$?

Smoothness of distance function in Riemannian Manifolds

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

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

The kissing number of a square, cube, hypercube?

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

Diameter of m-fold cover

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

Zariski closed sets in C^n are of measure 0

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

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

Set theory in practice

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

Convex Hull of Path Connected sets

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

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

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

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

Geodesics of bounded length on a Riemannian manifold

To what extent is convexity a local property?

Are there unique geodesics in the NIL and SOL geometry?