He is also one of the greatest scientists in history, having worked on mathematics, mechanics, optics and many other fields. As a mathematician, he has elaborated the modern concept of mathematical function, which he derived from his research on set theory (d'you remember good old Cartesian Product ?). He also discovered (among others) some of optics' fundamental laws (including the famous principle stating that "light always chooses the quickest path between two points"). Laws of refraction bear his name in many countries (you can also find them under the name of "Snell laws").