The Radio Interference problem: given the locations of n radio broadcasting centers and their broadcasting power, assuming they all use the same radio frequency channel, we want to determine whether there is any radio interference between them. More specifically, suppose we are given the xy-coordinates of each of these n centers in the plane, and we assume that their radio signals can propagate up to a given distance D in all directions in the plane. The problem is to determine whether there is any point in the plane that can receive a radio signal from more than one of these centers. This problem can be solved most efficiently in the worst case in (?) time.