Title: Optimally Gathering Two Robots,
Abstract: We present an algorithm that ensures in finite time the gathering of two
robots in the non-rigid ASYNC model. To circumvent established impossibility
results, we assume robots are equipped with 2-colors lights and are able to
measure distances between one another. Aside from its light, a robot has no
memory of its past actions, and its protocol is deterministic. Since, in the
same model, gathering is impossible when lights have a single color, our
solution is optimal with respect to the number of used colors.