Appel, K.; Haken, W. Every planar map is four colorable. I: Discharging. (English) Zbl 0387.05009 Ill. J. Math. 21, 429-490 (1977). Page: −5 −4 −3 −2 −1 ±0 +1 +2 +3 +4 +5 Show Scanned Page Cited in 11 ReviewsCited in 326 Documents MSC: 05C15 Coloring of graphs and hypergraphs PDFBibTeX XMLCite \textit{K. Appel} and \textit{W. Haken}, Ill. J. Math. 21, 429--490 (1977; Zbl 0387.05009) Online Encyclopedia of Integer Sequences: Chromatic number (or Heawood number) of nonorientable surface with n crosscaps. Chromatic number (or Heawood number) Chi(n) of surface of genus n.