 (Let me mention a similar paradox of motion—the ‘millstone’—attributed to Maimonides. Imagine two wheels, one twice the radius and circumference of the other, fixed to a single axle. Let them run down a track, with one rail raised to keep the axle horizontal, for one turn of both wheels [they turn at the same rate because of the axle]: each point of each wheel makes contact with exactly one point of its rail, and every point of each rail with exactly one point of its wheel. Does the assembly travel a distance equal to the circumference of the big wheel? Of the small? Both? Something else? How? This problem too requires understanding of the continuum; but it is not a paradox of Zeno’s so we shall leave it to the ingenuity of the reader.) 