Two mathematicians at the University of Illinois, Kenneth Appel and Wolfgang Haken, solve the four-color problem. Or: Is it possible to draw a political map with a minimum number of colors greater than four? (Without allowing two countries bordering at more than one point to have the same color). Appel and Haken reduce the problem to a computer analysis of 1,500 different base maps. After 1,200 hours of computer time, the computer produces the result: each map can be colored with only four colors. Guthrie’s intuition (1852!) is thus confirmed.
