18,681 reputation
361144
bio website math.psu.edu/petrunin
location Penn State
age 47
visits member for 5 years, 8 months
seen 22 hours ago

A description by my son:

Mein Vater hat keine Haare aber er hat einen schwarzen Bart. Er hat grüne Augen so wie ich. Er benutzt seine Brille sehr selten. Sein Name ist Tosha. Er mag Musik spielen aber ist ganz schlecht dabei und ist 44 Jahre alt.


Jul
3
comment How to prove the existence of the polytope in $\mathbb{R}^d$ with a given number of faces, minimizing the isoperimetric ratio?
It follows since the space of configurations of $n$ unit vectors is compact.
Jul
2
answered Is the boundary of an open, regular, bounded, path-connected, and simply connected set a Jordan curve
Jun
27
awarded  Notable Question
Jun
11
comment Gauss-Bonnet formula for 2-dimensional Alexandrov spaces
Yes, GH-continuity is missing in the ref, but it follows easily.
Jun
9
comment How misleading is it to regard $\frac{dy}{dx}$ as a fraction?
I do not think you should remind that y is a function of x if it is not necessary; so for me this is a feature!bug.
Jun
5
comment Alexandrov spaces which are not limits of Riemannian manifolds
in (2) you get examples which are compact and which are not compact.
Jun
4
revised Alexandrov spaces which are not limits of Riemannian manifolds
added 47 characters in body
Jun
4
comment Alexandrov spaces which are not limits of Riemannian manifolds
(1) yes always, (2) the construction is local and one can assume $A$ is compact,
Jun
3
awarded  Notable Question
Jun
3
answered Alexandrov spaces which are not limits of Riemannian manifolds
Jun
3
revised Euclid with Birkhoff
added 13 characters in body
May
31
asked Nice applications of Liouville's theorem
May
27
revised Suggestions for good notation
added 4 characters in body
May
25
awarded  Nice Answer
May
22
comment Does the Riemann-Christoffel curvature determine the connection?
For the connections with torsion the question gets easier.
May
22
comment Perturb a given smooth function to a Morse function relative to fixed level sets, which are already fine
@Francis: Now it is corrected.
May
22
revised Perturb a given smooth function to a Morse function relative to fixed level sets, which are already fine
added 18 characters in body
May
21
revised Perturb a given smooth function to a Morse function relative to fixed level sets, which are already fine
added 68 characters in body
May
21
answered Perturb a given smooth function to a Morse function relative to fixed level sets, which are already fine
May
15
comment Fundamental groups of stably parallelizable manifolds
@QiaochuYuan, For closed you can take the doubling and realize it as a hypesurface in $\mathbb R^{n+1}$, the result is stably parallelizable.