We generalize the Five-Color Theorem by showing that it extends to graphs with two crossings. Furthermore, we show that if a graph has three crossings, but does not contain K(6) as a subgraph, then it is also 5-colorable. We also consider the question of whether the result can be extended to graphs with more crossings. (C) 2008 Elsevier B.V. All rights reserved.
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页码:2948 / 2951
页数:4
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Kleitman D. J., 1970, Journal of Combinatorial Theory, Series A, V9, P315, DOI 10.1016/S0021-9800(70)80087-4