Let
be a collection of circles in the Riemann sphere
that bound disjoint open disks
.
Note that circles may be tangent,
but otherwise they don't intersect.
(See Figure 1.)
Figure 1: Circles in the Riemann sphere.
Let F denote the complement of
,
that is,
the closure of the common exterior of
.
Suppose that n is even,
and that for
we have specified a Mobius transformation
mapping the exterior of 
to the interior of 
.
The group 
of Mobius transformations
generated by the 's
is a Kleinian group with fundamental domain F.
It is called a
classical Schottky group.