. "(diagram 1) And so let there be magnitudes, however many, placed successively, A, B, G, D, E each four-times its follower, and let A be largest and let Z be a third of B, H of G, Q of D, and I of E. (diagram 2) And so, since Z is a third part of B, and B is a fourth part of A, both together, B, Z, are a third part of A. (diagram 3) And for the same reasons, in fact, H, G is a third part of B, and" . . . .