bio  website  math.psu.edu/petrunin 

location  Penn State  
age  46  
visits  member for  5 years, 1 month 
seen  3 hours ago  
stats  profile views  10,852 
A description from 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.
11h

revised 
Is the “Napkin conjecture” open? (origami)
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2d

revised 
Nonperiodic points of piecewiselinear homeomorphisms
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Dec 19 
revised 
Diameter of mfold cover
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Dec 19 
comment 
Is the blowing up the rectifiable set cone?
Well first formulate the question correctly :) 
Dec 19 
awarded  Nice Answer 
Dec 18 
comment 
Is the blowing up the rectifiable set cone?
The question is not formulated well, but it seems that the answer is NO for any reformulation. 
Dec 18 
comment 
Nonperiodic points of piecewiselinear homeomorphisms
@JamesPropp: the answer is updated. 
Dec 18 
revised 
Nonperiodic points of piecewiselinear homeomorphisms
added 291 characters in body 
Dec 18 
comment 
Nonperiodic points of piecewiselinear homeomorphisms
@JamesPropp, I do not see how bounty may help here, you should tell what is not clear  then I can help. 
Dec 16 
comment 
Nonperiodic points of piecewiselinear homeomorphisms
@JamesPropp: if a point $x\in \triangle'$ is close to the base of $\triangle'$ then $T^n$ moves it slowly. So number of iterations of $T^n$ keeps the point in $\triangle'$ and the orbit $x_k=T^{n\cdot k}(x)$ is very predictable. 
Dec 13 
comment 
Nonperiodic points of piecewiselinear homeomorphisms
P.S. Nice question, can you tell why did you need it? 
Dec 13 
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Nonperiodic points of piecewiselinear homeomorphisms
@JamesPropp: Given a poisitive integer $K$ you can find an open rectangle $\square$ near the base of $\triangle'$ such that $\square\cap E_k=\varnothing$ for any $k<K$. 
Dec 12 
revised 
Nonperiodic points of piecewiselinear homeomorphisms
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Dec 12 
answered  Nonperiodic points of piecewiselinear homeomorphisms 
Dec 7 
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What introductory book on Graph Theory would you recommend?
I used this book to teach a course this semester, the students liked it and it is a very good book indeed. [The book includes number of quasiindependent topics; each introduce a brach of graph theory and avoids tecchnicalities. I would include in addition basic results in algebraic graph theory, say Kirchhoff's theorem, I would expand the chapter on Algorithms, but the book is VERY GOOD anyway.] 
Dec 2 
comment 
Besicovitch's covering theorem for ellipsoids and shadows
Check this answer, it seems to be related mathoverflow.net/a/127928 
Nov 27 
revised 
another question about connected open sets in $R^2$
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Nov 27 
answered  another question about connected open sets in $R^2$ 
Nov 24 
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Normal Variation on Manifolds
OK, you want to bound the Lipschitz constant of the Gauss map in terms of normal curvatures. This is a question in linear algebra. Set $q(x,y,z,w)=\langle s(x,y),s(z,w)\rangle$ then you get all the values $q(x,x,x,x)$ and you need to estimate $\sum q(u,e_i,u,e_i)$, but I am too lazy. 
Nov 24 
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Normal Variation on Manifolds
@user62013 Well, the "principle curvatures" are not defined if codimension $>1$. 