16,503 reputation
351133
bio website math.psu.edu/petrunin
location Penn State
age 45
visits member for 4 years, 5 months
seen 6 hours ago

From my son's writing:

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.


11h
answered Are the higher homotopy groups of the Hawaiian earring trivial?
18h
comment Dimension of a set detected by a homology class
@IgorBelegradek, All this follows directly from the construction.
18h
comment Dimension of a set detected by a homology class
@IgorBelegradek, I think all this standard, isn't it? I only wanted to indicate the construction.
19h
revised Dimension of a set detected by a homology class
+pic
1d
answered Dimension of a set detected by a homology class
2d
comment Length inequalities in trees and CAT(0) spaces
Close, but not the same. We ment something like that: mathoverflow.net/questions/7794/ (you will not need the consition on rank. For Lobachevsky space or sphere you need to use hyperbolic/spherical cosine rule instead.)
2d
reviewed Approve suggested edit on Projective modules over noncommutative tori?
2d
reviewed Approve suggested edit on Drinfeld's noncommutative projective line and noncommutative geometry
2d
answered Length inequalities in trees and CAT(0) spaces
Apr
1
comment A question on the curvature of smooth and embedded curves in a plane
No, check the picture in this question: mathoverflow.net/questions/126128/…
Mar
31
awarded  Nice Answer
Mar
25
comment Isometric embedding of SO(3) into an euclidean space
This is the same as the Veronese embedding $\mathbb{R}\mathrm{P}^3\hookrightarrow \mathbb{R}^9$.
Mar
25
comment Isometric embedding of SO(3) into an euclidean space
@MarianoSuárez-Alvarez OP did not specify the class of embeddings, if it is $C^1$ then by Nash--Kuiper there is one, for $C^\infty$-embeddings 9 might be the best.
Mar
24
comment Buseman function for Riemanniam manifolds with two ends and $Ric\ge -(n-1)$
No, take double punctured torus (complete metric with constant curvature and finite volume).
Mar
24
comment Ricci curvature under rough convergence
@ChrisGerig, I do not see ambiguity in the question. In fact it takes some effort to formulate the collapsing version of the statement without optimal transport (try to do this).
Mar
24
revised Ricci curvature under rough convergence
deleted 2 characters in body
Mar
23
comment Ricci curvature under rough convergence
P.S. also, it should be known that if $m$-dimensional manifolds with lower bound for Ricci curvature GH-converge to an $m$-dimensional manifold then it converges in measured Gromov--Hausdorff sense. It is Colding's result if I remember right, likely he also proved the statement you asked.
Mar
23
answered Ricci curvature under rough convergence
Mar
21
awarded  Nice Answer
Mar
17
reviewed Approve suggested edit on Gödel's Constructible Universe in Infinitary Logics (A Possible Approach to HOD Problem)