  We present a decentralized algorithm to achieve segregation into an arbitrary
number of groups with swarms of autonomous robots. The distinguishing feature
of our approach is in the minimalistic assumptions on which it is based.
Specifically, we assume that (i) Each robot is equipped with a ternary sensor
capable of detecting the presence of a single nearby robot, and, if that robot
is present, whether or not it belongs to the same group as the sensing robot;
(ii) The robots move according to a differential drive model; and (iii) The
structure of the control system is purely reactive, and it maps directly the
sensor readings to the wheel speeds with a simple 'if' statement. We present a
thorough analysis of the parameter space that enables this behavior to emerge,
along with conditions for guaranteed convergence and a study of non-ideal
aspects in the robot design.
