Kenneth Appel, a mathematician who was the first to use a computer to prove a major mathematical theorem, passed away on April 19 in Dover, New Hampshire. He was 80 years old and died from esophageal cancer.

He and Wolfgang Haken used 1,200 calculations from an IBM computer to prove that a flat map can be colored with only four colors, so that contiguous countries have different colors. Thus they proved the 100-year-old "Four-Color Conjecture." Many mathematicians at the time did not trust the performance of computers and were not quick to believe Appel had accomplished the major achievement. They feared computer bugs and reliance on a mathematical proof without any physical evidence.

At the time, the New York Times called this "a major intellectual feat."

"It gives us an important new insight into the nature of two-dimensional space and of the ways in which such space can be broken into discrete portions," the article continued.

Appel and Haken received the American Mathematical Society and the Mathematical Programming Society's Delbert Ray Fulkerson prize in 1979.

Appel was an educator for most of his life. He chaired the University of New Hampshire mathematics department before retiring in 2003. Since then, Appel taught students at Dover High School by helping them to set up an Internet-based homework system. He served on the Dover Board of Education.

Born on October 8, 1932 in Brooklyn, New York, Appel grew up in Queens and studied mathematics at Queens College. He served in the army and earned a doctorate in mathematics from the University of Michigan. He then turned to research in cryptography at the Institute for Defense Analyses before moving on to the University of Illinois.