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Sergei Ivanov
  • Member for 12 years, 5 months
  • Last seen more than a month ago
119 votes
Accepted

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

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?

67 votes

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

62 votes
Accepted

Smoothness of distance function in Riemannian Manifolds

61 votes
Accepted

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

45 votes
Accepted

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

41 votes
Accepted

Why are free groups residually finite?

40 votes
Accepted

When factors may be cancelled in homeomorphic products?

37 votes

Linearity of the inner product using the parallelogram law

37 votes

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

35 votes
Accepted

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

33 votes
Accepted

The kissing number of a square, cube, hypercube?

33 votes
Accepted

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

26 votes
Accepted

Diameter of m-fold cover

26 votes
Accepted

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

25 votes
Accepted

Zariski closed sets in C^n are of measure 0

24 votes

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

24 votes
Accepted

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

24 votes
Accepted

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

23 votes
Accepted

Microwaving Cubes

22 votes

Set theory in practice

21 votes

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

21 votes

Convex Hull of Path Connected sets

20 votes
Accepted

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

19 votes
Accepted

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

19 votes
Accepted

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

19 votes
Accepted

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

18 votes
Accepted

Geodesics of bounded length on a Riemannian manifold

18 votes
Accepted

To what extent is convexity a local property?

17 votes
Accepted

Are there unique geodesics in the NIL and SOL geometry?

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