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Search options questions only not deleted not community wiki created 2011-09-28 - 2012-09-28
9 votes
2 answers
440 views

From very many sets of fixed measure in a probability space, can we select many that have a ...

I assume the following Lemma is either well known or, more probably, a Corollary of a much stronger well known Theorem, and I would be grateful for a reference: For all $\delta\in (0,1)$ and all $\el …
Jakob's user avatar
  • 894
13 votes
4 answers
930 views

Translation distance in the curve complex

Given a map $\psi: S\rightarrow S,$ for $S$ a closed surface, is there any algorithm to compute its translation distance in the curve complex? I should say that I mostly care about checking that the t …
Igor Rivin's user avatar
  • 96.4k
1 vote
2 answers
299 views

Galois extension of a semi-local ring

Hi, i would like to know if weather or not a Galois extension of a commutative semi-local ring is also a semilocal ring.
Hector's user avatar
  • 11
7 votes
0 answers
351 views

How does the number of self-avoiding paths between two points scale, in a square/cubic lattice?

Consider two different infinite graphs, whose vertices are drawn from $\mathbb Z^2$ or $\mathbb Z^3$. Let $P_d : \mathbb Z^d \times \mathbb N \to \mathbb N$ for $d \in \{2,3\}$ be the function such th …
Niel de Beaudrap's user avatar
7 votes
1 answer
652 views

Compactness of Sobolev embedding for domains of finite measure

Let $\Omega \subset \mathbb{R}^d$ be a domain of finite Lebesgue measure, not assumed to be smooth or bounded. Is it true that the embedding of, say, $W^{1,p}_0(\Omega)$ (Sobolev functions with zero b …
Alexander Shamov's user avatar
0 votes
2 answers
1k views

Finite projection in Von Neumann algebra

I had the following question when I am learning von Neumann algebras: Let p be a finite projection in a finite von Neumann algebra $M$, let $p>p_1>p_2>\cdots$ be a decreasing sequence of projections …
Qingyun's user avatar
  • 411
4 votes
2 answers
308 views

When is a torsionfree subgroup contained in a torsionfree direct summand?

Let $F$ be a torsionfree subgroup of a commutative group $G$. Are there nontrivial conditions known under which there exists a torsionfree direct summand of $G$ containing $F$? I would already be …
Fred Rohrer's user avatar
  • 6,700
11 votes
1 answer
585 views

Hopf algebras and bijective antipodes

By a theorem of Larson and Sweedler, the antipode of every finite-dimensional Hopf algebra is bijective. My question is the following: Is it true that in every noetherian Hopf algebra the antipode i …
warren's user avatar
  • 295
17 votes
1 answer
2k views

Representations attached to p-adic modular forms

A theorem of Gouvea and Hida (or rather a consequence of it) states that there exist a Galois representation attached to a $p$-adic eigenform $f$ provided the residual representation attached to a cla …
Arijit's user avatar
  • 995
16 votes
2 answers
3k views

Approximating a convex function by a piecewise linear function

Suppose I have a Lipschitz-continuous convex function $f:\mathbb{R}^n\rightarrow \mathbb{R}$. I wish to approximate it on the unit ball by a piecewise-linear function $g:\mathbb{R}^n\rightarrow \mathb …
Flavio Burton's user avatar
6 votes
4 answers
705 views

Higgs mechanism from a deformation quantization point of view

Is it possible to describe the Higgs mechanism from a deformation quantization point of view? How would one do it? Are there aspects of the Higgs mechanism and Higgs particle which one may see clearer …
student's user avatar
  • 1,222
6 votes
1 answer
1k views

Graham-Rothschild via Hales-Jewett

I am currently reading the recent preprint of Dodos, Kanellopoulos, Tyros, where the ambitiously short proof of Density Hales Jewett theorem is provided. The important ingredient is Graham-Rothschild …
Fedor Petrov's user avatar
22 votes
6 answers
2k views

Does every ellipse inside a tetrahedron inside a ball fit in a triangle inside the ball?

In three-dimensional euclidean space, consider the closed unit ball $B$. Let $T$ be a tetrahedron, and $E$ an ellipse, with $E \subset T \subset B$. Does there necessarily exist a triangle $T'$ with $ …
Matt Pusey's user avatar
5 votes
3 answers
2k views

When is the graph of a function a dense set?

Let $f: \mathbb R \to \mathbb R$ be any function. When is the graph of $f$ dense in $\mathbb R^2$? The only examples I know for this are for non-measurable functions, but is that a necessary condition …
Anindya's user avatar
  • 53
1 vote
0 answers
184 views

Fields over which cubic hypersurfaces are rational

All cubic hypersurfaces having at least one double point are birational to some $P^n$ over an algebraically closed field. How does the statement change as I pass to non alg closed fields? Does it hold …
IMeasy's user avatar
  • 3,779

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