Four race car drivers participate in a race on a loop track. All four are going at a constant speed. Assume that they did a flying start. That is, all four crossed the start line at the same instant while each was going their constant speed. Then they continue driving forever and it is the case that for any three of the cars there is a moment in time, after the start, when these three cars are located at the same point along the track (all three are passing each other). Prove that there is a moment in time, after the start, when all four cars are located at the same point along the track.