The four-color map problem was first posed by Francis Guthrie (1831–1899) in 1852. While coloring a map of the English counties, Guthrie discovered he could do it with only four colors and no two adjacent counties would be the same color. He extrapolated the question to whether every map, no matter how complicated and how many countries are on the map, could be colored using only four colors with no two adjacent countries being the same color. The theorem was not proved until 1976, 124 years after the question had been raised, by Kenneth Appel (1932–) and Wolfgang Haken (1928–). Their proof is considered correct although it relies on computers for the calculations. There is no known simple way to check the proof by hand.