Every planar map is four colorable. (English) Zbl 0331.05106
MSC:
| 05C15 | Coloring of graphs and hypergraphs |
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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