"The Platonic doctrine of reminiscence is then adduced as a confirmation of the pre-existence of the soul. Some proofs of this doctrine are demanded. One proof given is the same as that of the Meno, and is derived from the latent knowledge of mathematics, which may be elicited from an unlearned person when a diagram is presented to him."
got a little hung up on this since I didn't really see the "proof" spoken of. found the wiki page, Plato's Problem and read that the math in this case had be the Pythagorean proposition... which is interesting and packed with it's own history... plus, I could use a reminder so I'm adding it