If all bodies are equal in number and magnitude and in the starting positions above, it follows that when rows B and C move to the opposite ends of the stadium, the first C has passed all the Bs, and the first B has passed only two As, but has passed all the Cs. Assuming each body must be opposite every body it passes for an equal amount of time; the first B takes only half the time to pass half the As as the first C takes to pass all the Bs. Therefore, the time it takes to pass half the As is also half the time it takes to pass all the Cs, so the first Bs passage past half the As takes both the same time and half the time as its passage past the Cs.