## All Questions

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 …
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 …
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### 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.
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 …
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 …
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 …
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 …
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 …
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 …
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. …
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 …
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 …
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 …