Appel, K.; Haken, W.; Koch, J. Every planar map is four colorable. II: Reducibility. (English) Zbl 0387.05010 Ill. J. Math. 21, 491-567 (1977). Page: −5 −4 −3 −2 −1 ±0 +1 +2 +3 +4 +5 Show Scanned Page Cited in 11 ReviewsCited in 276 Documents MSC: 05C15 Coloring of graphs and hypergraphs PDFBibTeX XMLCite \textit{K. Appel} et al., Ill. J. Math. 21, 491--567 (1977; Zbl 0387.05010)