# Tagged Questions

**14**

votes

**0**answers

614 views

### New(?) reciprocity law

Consider three functions $f, g$ and $h$ on a smooth curve $X$ over $\mathbb{C}$.
I have found the following equality:
$$\sum (res(f\frac{dg}{g})\frac{dh}{h}-res(f\frac{dh}{h})\frac{dg}{g})=0.$$
Here ...

**1**

vote

**0**answers

127 views

### Hopf lemma for line bundles on curves in algebraic geometry

In the paper http://arxiv.org/pdf/math/0110256v1.pdf Claire Voisin proves that all linear subspaces which lie inside of a (not too big) secant variety of a smooth projective curve must lie inside one ...

**5**

votes

**2**answers

681 views

### “Arithmetic genus” of a plane curve singularity.

I believe that the following questions are very basic, but I don't know how to get a reference.
Consider a curve in the plane $C\in \mathbb C^2$ with a singularity at $0$ and suppose it is
...

**3**

votes

**1**answer

409 views

### Name for curve?

I am doing something with the curve given parametrically by
$y = (-ar+b) r$, $x = \sqrt{r^2-y^2}$
for $r\in \lbrack (b-1)/a,b/a\rbrack$. It is nice enough (and of low enough degree) that I suspect ...

**1**

vote

**1**answer

179 views

### invariants of plane quartics

Does anybody know a good reference where the invariants for plane quartic curves are developed?

**7**

votes

**0**answers

403 views

### Elementary proof of the Hurwitz formula

I am aware of two forms of the Hurwitz formula. The first is more common, and deals only with the degrees. So if $f:X \rightarrow Y$ is a non-constant map of degree $n$ between two projective ...

**1**

vote

**1**answer

153 views

### pull back of hodge bundle via glueing map

Hi,
I need a precise reference for the following fact, which is certainly well known, but I do not find any.
I consider the natural glueing map of pointed curves $\overline{M}_{g_1,n}\times ...

**3**

votes

**0**answers

220 views

### Igusa-Clebsch invariants

I am looking for a good reference for definitions and basic properties of the Igusa-Clebsch invariants for curves of genus $2$ (especially, but not only, in positive characteristic).

**2**

votes

**2**answers

337 views

### Recognize this plane curve?

An aspect of my work led to a plane curve with implicit equation
$$
x^2+y^2 = 3 (y/2)^{2/3} + 1
$$
Actually, I started with the parametrization below and derived from it the
equation above:
...

**9**

votes

**0**answers

439 views

### Function fields of characteristic p modular curves, and mod p reductions of the classical modular equation

Let l and p be distinct primes, l>2. There are "characteristic p modular curves" X_0(l) and X(l), defined over an algebraic closure, K, of Z/p, solving moduli problems for elliptic curves with some ...

**1**

vote

**2**answers

444 views

### Weil bound for characters sums. (reference-request )

Do you know on any good reference on Weil bound for charcter sums over algebraic curves.
I prefer reference which assume few previous knowlage.

**1**

vote

**3**answers

622 views

### Are the arithmetic genera of Cohen-Macaulay curves in a fixed homology class bounded?

Let X be a smooth projective variety over the complex numbers. Recall that a Cohen-Macaulay curve is a one-dimensional closed subscheme without embedded or isolated points (fat components are ...