Kenneth Appel | Mathematician, 80

Kenneth Appel, 80, a mathematician who was the first to use a computer to prove a century-old major mathematical theorem, has died in Dover, N.H.

The Tasker Funeral Home confirms that Mr. Appel, who had esophageal cancer, died April 19.

Mr. Appel was a longtime educator who chaired the University of New Hampshire's mathematics department, retiring in 2003.

Before that, he was a faculty member at the University of Illinois at Urbana. In 1976, he and Wolfgang Haken used 1,200 hours of calculations from an IBM computer to prove that a flat map can be colored with just four colors so that contiguous countries have different colors.

Proving the 100-year-old "four-color conjecture" was considered a major intellectual accomplishment. - AP