Conformal map of polygon with circle segments I am looking for a conformal map from a "polygon" to eg the upper half plane, which consists of circle segments instead of lines. So for example, it could be a quadrilateral ABCD, but where AB is a circle segment. The closest I can find is the Schwarz-Christoffel mapping. 
Anyone has any tips?
 A: The mapping function is a solution of the Schwarz differential equation
$$\frac{f'''}{f'}-\frac{3}{2}\left(\frac{f''}{f'}\right)^2=R(z),$$
where $R$ is a rational function with poles at the preimages of the vertices. The poles of $f$ are of second order, and the coefficients at the second order terms are determined by the angles. Schwarz equation can be reduced to a linear differential equation of the form
$y''+Ry/2=0$. In the case of a triangle, this is a hypergeometric equation.
In the case of a quadrilateral, this is a Heun equation.
Literature: Courant, Geometrische Funktionentheorie,
Caratheodory, Funktionentheorie, II, (There is an English translation),
Golubev, Vorlesungen über Differentialgleichungen im Komplexen, (transled from Russian).
The case of a triangle is completely understood (see any book on hypergeometric function)
The case of a quadrilateral is already quite complicated, and there are many
unsolved questions about quadrilaterals and Heun's equation. See for example  arXiv:1409.1529 for some recent results about this, and literature there.
EDIT. More concrete examples can be found here  arXiv:1111.2296 and here  arXiv:1110.2696
and in references to these papers.
