. . . . . . . . . "1932-10-08Z"^^ . "Appel, Kenneth"@en . "1932Z"^^ . "Kenneth Ira Appel"@en . . "Americanmathematician" . "2013-04-19Z"^^ . "2013Z"^^ . . . . "Kenneth Ira Appel (October 8, 1932 \u2013 April 19, 2013) was an American mathematician who in 1976, with colleague Wolfgang Haken at the University of Illinois at Urbana-Champaign, solved one of the most famous problems in mathematics, the four-color theorem. They proved that any two-dimensional map, with certain limitations, can be filled in with four colors without any adjacent \"countries\" sharing the same color."@en . . .