S> The SmalleSt number of colourS neceSSary to colour the nodeS of a graphSo that no two adjacent nodeS have the Same colour. See alSo: four colour map theorem. {Graph Theory LeSSonS (http://www.utc.edu/~cpmawata/peterSen/leSSon8.htm)}. {Eric WeiSStein' S World Of MathematicS (http://mathworld.wolfram.com/ChromaticNumber.html)}. {The Geometry Center (http://www.geom.umn.edu/~zarembe/grapht1.html)}. (2000-03-18)