Linda talks to Dr. Ronald Graham, a mathematician and director of Information Sciences Research at AT&T Laboratories, about his friend Paul Erdos, who died Friday at the age of 83 following a heart attack. Erdos is considered by many to be the greatest mathematician of his generation. The 83-year-old Hungarian-American died in Warsaw. Graham says Erdos considered himself the Johnny Appleseed of Math, spreading knowledge from place to place. Erdos had neither home nor job. He went from place to place, staying with colleagues, before moving on after a few days.