(CNN) -- Even by MIT standards, says Tom Leighton, Danny Lewin was special. "He was really exceptionally smart. MIT has a lot of really smart people, and Danny stood out even among that rarified environment," says Leighton, who was then one of Lewin's professors at the Massachusetts school's computer science laboratory. That kind of determination drove Lewin throughout his short life. He was an American who joined the Israeli army and served in an elite unit, though he could have avoided the military altogether. He was a mathematician who could have had a stellar academic career but decided to jump...