Kenneth Appel
1932–2013, Brooklyn, New York, United States, Dover, New Hampshire, United States
American mathematician who, with Wolfgang Haken, proved the four colour theorem in 1976 using an early computer-assisted case analysis.
Kenneth Appel was born in Brooklyn, New York, and earned his PhD in mathematics from the University of Michigan in 1959 under Roger Lyndon, after working as an actuary and serving in the U.S. Army. He joined the mathematics faculty of the University of Illinois at Urbana-Champaign in 1961.
With his colleague Wolfgang Haken, Appel spent years developing a strategy to reduce the four colour conjecture — first posed in 1852 — to a finite, checkable set of map configurations. In 1976 the two announced a proof: any potential counterexample had to contain one of 1,936 unavoidable configurations, and an IBM computer checked each configuration over more than a thousand hours of processing time. It was the first major theorem whose proof depended essentially on a computer, and it started a long debate about what counts as a mathematical proof.
Appel and Haken shared the Fulkerson Prize in 1979 for this work. Appel later chaired the mathematics department at the University of New Hampshire, retiring in 2003. He died in Dover, New Hampshire, in 2013.
Workplaces: University of Illinois at Urbana-Champaign, University of New Hampshire
United States