## All Questions

0answers
164 views

### 12 and 13-bit balanced Gray codes

I am trying to find a transition sequence for both 12 and 13 bit balanced Gray codes. I know there are some excellent papers on the topic of deriving these sequences available on t …
1answer
213 views

### Asymptotics for forbidden subwords

Fix an alphabet $A$ and consider words of length $n$ over $A$. Fix a set $B$ of $k$ forbidden subwords (subword is not necessarily connected, i.e. $abb$ is a subword of $abcb$). Ca …
0answers
275 views

### elementary Abel function of a polynomial

Is there an elementary real function $F$ such that $F(1+F^{-1}(x))$ is a polynomial of degree at least 2 without real fixpoints.
0answers
204 views

### About Michael Barr immersion theorem for regular categories, and pretopos

In the article of M. Barr "Representation of Categories" J. Pure Appl. Algebra, 41 (1986), 113–137 link: ftp://ftp.math.mcgill.ca/pub/barr/pdffiles/represen.pdf M. Barr shows a c …
1answer
461 views

### subgroups of graph groups

Let $G$ be a graph group and let $S$ be a finitely generated subgroup of $S$. What torsion can $H_1(S)$ have? Let me put this in context: Let $Y$ be a graph, then the correspondin …
2answers
500 views

### Proper definition of a moduli problem

This question arose after I thought about Ben Webster's comments to this question. There he asked me what was my definition of a moduli problem. When I came to think of it, I neve …
1answer
443 views

### Surgery and homology: a reference request

I need a reference (or a short proof) for the following statement: Suppose a closed manifold $N$ is the result of a surgery (along an embedded sphere) on a closed manifold $M$. Th …
2answers
479 views

### elementary equivalence of infinitary symmetric groups

Two questions: Suppose a and b are two uncountable cardinals. Consider the symmetric groups on sets of sizes a and b respectively (the symmetric group on a set is the group of al …
5answers
584 views

### Tetrad postulate: Implies or results from the metricity of the connection?

Hi, I see that the tetrad postulate: $\nabla_{\mu}e_{\nu}^{I}=\partial_{\mu}e_{\nu}^{I}-\Gamma_{\mu\nu}^{\rho}e_{\rho}^{I}+\omega_{\mu J}^{I}e_{\nu}^{J}=0$ Can be merely derived …
1answer
178 views

### extension of a vector bundle over punctured relative curve

Let $C$ be a curve (smooth projective over a field $k$ of positive char) and $p$ a rational point on $C$. Put $\dot{C}=C-{p}$ and $T=Spec R$, where $R$ is a noetherian $k$-algebra. …
2answers
741 views

### computation, algebra, logic

So a really simple way of describing a digital computer is to say that it is a device for performing boolean operations. You feed it a bunch of bit strings, which is a description …
1answer
303 views

### Automorphisms of $\pi_1$ induced by pseudo-Anosov maps

Suppose $X$ is an orientable surface with non-empty boundary and $f:X\to X$ is a pseudo-Anosov automorphism that acts identically on $H_1(X,\mathbf{Z})$. Let $x$ be a fixed point o …
0answers
235 views

### solving polynomials [closed]

Hello. While trying to find out how to find all the roots of any polynomial equation someone said this,"At least for real roots it can be completely solved by bracketing zeroes wit …
2answers
369 views

### Applications of classifying thick subcategories

So, relatively recently, Balmer introduced this notion of a spectrum for a tensor triangulated category and used it to prove a generalization of a classification theorem done in se …
2answers
444 views

### Why does twisting quasi-Hopf algebras work (as in majid’s article)

I can't understand this sentence i the article of Majid "Tannaka-Krein theorem for quasi-Hopf algebras and other results" about the reconstruction of a quasi-algebra (in fact its d …

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