Abraham Lincoln famously learned every proof in Euclid's elements in order to fine tune his mind. So you can really view Euclid as the father of geometry. But that's not all. There are many other contributors in philosophy and math. And this is just, once again, a sample of all of the folks who contributed. On the side of philosophy, you have Xenophon, who is another one of Socrates' students in addition to Plato. And in fact, the life of Socrates, we learn from the writings of Plato and Xenophon.