Every planar map is four colorable. (English) Zbl 0331.05106


05C15 Coloring of graphs and hypergraphs
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[2] K. Appel and W. Haken, The existence of unavoidable sets of geographically good configurations, Illinois J. Math. 20 (1976), no. 2, 218 – 297. · Zbl 0322.05141
[3] Heinrich Heesch, Untersuchungen zum Vierfarbenproblem, B. I. Hochschulskripten, vol. 810/810, Bibliographisches Institut, Mannheim-Vienna-Zürich, 1969 (German). · Zbl 0187.20904
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