An Apollonian net. Given three mutually tangent circles, it is possible to construct two other circles tangent to all three. One of the five circles bounds the other four. This algorithm is a special case of one discovered by the Greek mathematician Apollonius of Perga. The process is repeated for each triple of tangent circles, and so on ad infinitum. The figure that results is called an Apollonian net; the figure bounded in the circular “triangle” of three tangent circles is called an Apollonian gasket.