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


MSC:

05C15 Coloring of graphs and hypergraphs
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Online Encyclopedia of Integer Sequences:

Chromatic number (or Heawood number) Chi(n) of surface of genus n.

References:

[1] . F. Allaire and E. R. Swart, A systematic approach to the determination of reducible configurations, J. Combinatorial Theory Ser. B (to appear). · Zbl 0398.05034
[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
[4] Hassler Whitney and W. T. Tutte, Kempe chains and the four colour problem, Utilitas Math. 2 (1972), 241 – 281. · Zbl 0253.05120
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