Saunders Mac Lane, one of the country's leading mathematicians and a professor at the University of Chicago for nearly four decades, has died. He was 95. He died April 14 in San Francisco after a long illness, according to a statement released Thursday by the university. In a landmark paper he co-authored with Samuel Eilenberg in 1945, Mac Lane developed new ways of thinking about mathematics _ introducing what are known as "categories," "functors" and "natural transformations," the statement said. "A very great deal of mathematics since then would quite literally have been unthinkable without that language," University of Chicago...