TRIANGULATIONS OF S 3 AND THE COLORING OF GRAPHS
TRIANGULATIONS OF S 3 AND THE COLORING OF GRAPHS
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S 3 的三角剖分和图形的着色
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发表时间:
2010
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通讯作者:
H. Onishi
中科院分区:
文献类型:
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作者:
H. Onishi
A simple necessary and sufficient condition is given for the vertices of a graph, planar or not, to be properly four-colorable. This criterion involves the notion of an "even" triangulation of S3 and generalizes, in a natural way, a corresponding criterion for the three-colorability of planar graphs. 0. Introduction. With the Appel-Haken solution to the Four Color Problem [2], the question remains open of characterizing those graphs, planar or not, that are 4-colorable. This paper represents a step toward a solution by offering a new criterion for the 4-colorability of a graph embedded in 3-space, which was suggested by an analogous criterion for the 3-colorability of a graph embedded in the plane. The main result is that a graph in the 3-sphere S3 is (vertex) 4-colorable if and only if it is a subcomplex of the 1-skeleton of an "even" triangulation of S^-one in which every edge has an even number of faces incident to it. The corresponding result one dimension lower is well known [4, Theorem 7.4.3]. In §1, we present a summary of this theory with some auxiliary results, and in §2 we present the parallel theory in 3 dimensions. Since the original submission of this paper, Robert D. Edwards has announced an (independent) proof of the main result, following an idea of P. Deligne, R. MacPherson, and J. Morgan (see Notices Amer. Math. Soc. 24 (1977), A-257). The beautiful sequence of papers by Steve Fisk entitled Geometric coloring theory, which has begun appearing still more recently in Advances in Math. (24 (1977), 298-340, et seqq.), also contains ideas which overlap ours to some extent. We express our gratitude to the referee for his helpful suggestions about tightening the exposition of the paper. Received by the editors January 3, 1977 and, in revised form, October 25, 1977 and April 24, 1978. AMS (MOS) subject classifications (1970). Primary 05C15; Secondary 05C10, 55A15. © American Mathematical Society 1979