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

The Tasker Funeral Home confirms that Appel, who was diagnosed with esophageal cancer, died April 19 in hospice care.

Appel was a longtime educator who chaired the University of New Hampshire 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.

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