# Web of spheres

The collection of all spheres for which a given point (the centre of the web, or the radical centre) has a given power $p$ (the power of the web). There are three types of webs of spheres:

1) a hyperbolic web $(p>0)$, consisting of all spheres orthogonal to a given sphere;

2) an elliptic web $(p<0)$, consisting of all spheres intersecting a given sphere in a great circle of the latter;

3) a parabolic web $(p=0)$, consisting of all spheres passing though a given point.

The collection of all spheres common to two webs is called a net of spheres. The collection of all common spheres to three webs with centres not on a straight line is called a pencil of spheres.