Every planar graph can be properly vertex-coloured with ≤ 4 colours. First major theorem proved by computer (Appel-Haken, 1976; Robertson-Sanders-Seymour-Thomas, 1997).
Every planar graph can be properly vertex-coloured with ≤ 4 colours. First major theorem proved by computer (Appel-Haken, 1976; Robertson-Sanders-Seymour-Thomas, 1997).