Saunders Mac Lane, developed key algebraic theory; at 95

CHICAGO -- Saunders Mac Lane, one of the nation's leading mathematicians and the developer of an abstract algebraic theory that has applications in fields ranging from computer science to linguistics, died April 14 in San Francisco. He was 95.

In a landmark paper he co-wrote with Samuel Eilenberg in 1945, Dr. Mac Lane detailed what came to be known as the category theory. They sought to create a way to frame how different mathematic structures relate with each other and how they can predict or describe natural transformations.

''In fact, a very great deal of mathematics since then would quite literally have been unthinkable without that language," mathematics professor Peter May said in a statement released by the University of Chicago, where Dr. Mac Lane taught for more than three decades.

Dr. Mac Lane also wrote extensively on the history of mathematics, said Peter Johnstone, another mathematics professor at the University of Chicago.

He said Dr. Mac Lane ''left a unique body of material for future historians of 20th century mathematics, written by someone who was there at the time and who knew what it was like to be working at the cutting edge of mathematical research."

Dr. Mac Lane, who was born in Norwich, Conn., earned a bachelor's degree from Yale University and a master's from the University of Chicago. He received his doctorate in 1934 from the Mathematics Institute in Gottingen, Germany.

He taught at Harvard University from 1934 to 1947, when he joined the University of Chicago.

He wrote or co-wrote six books.

He received the nation's highest award for scientific achievement, the National Medal of Sciences, in 1989.

Dr. Mac Lane's first wife, Dorothy, died in 1985. He leaves his wife, Osa; two daughters, Gretchen of New York City and Cynthia Hay of London; and one grandchild.