Chilakamarri, K. "A 4-Chromatic Unit Distance Graph With No Triangles." 《Geomcombinatorics》 4, No. 3, 64-76, 1995.Exoo, G. 和 Ismailescu, D. "Small Order Triangle-Free 4-Chromatic Unit Distance Graphs." 《Geombinatorics》 26, No. 2, 49-64, 2016.Exoo, G. 和 Ismailescu, D. "The Chromatic Number of the Plane Is at Least 5--A New Proof." 2018 年 5 月 1 日。 https://arxiv.org/abs/1805.00157.Exoo, G. 和 Ismailescu, D. "A 6-Chromatic Two-Distance Graph in the Plane." 2019 年 9 月 29 日。 https://arxiv.org/abs/1909.13177.Hochberg, R. 和 O'Donnell, P. "Some 4-Chromatic Unit-Distance Graphs Without Small Cycles." 《Geombinatorics》 5, 137-141, 1996.Kiteck, D. 和 Payne, K. "A 21-Vertex 4-Chromatic Unit-Distance Graph of Girth 4." 《Ball State Undergraduate Mathematics Exchange》 15, No. 1, 2-9, 2021.O'Donnell, P. "A Triangle-Free 4-Chramatic Graph in the Plane." 《Geombinatorics》 4, No. 1, 23-29, 1994.O'Donnell, P. "A 40 Vertex 4-Chromatic Triangle-Free Unit Distance Graph." 《Geombinatorics》 5, No. 1, 30-34, 1995.Soifer, A. The Mathematical Coloring Book: Mathematics of Coloring and the Colorful Life of Its Creators. New York: Springer, 2008.Soifer, A. "Exoo-Ismailescu: The Final Word on Problem 15.4." Ch. 16 in The New Mathematical Coloring Book: Mathematics of Coloring and the Colorful Life of Its Creators, 2nd ed. New York: Springer, pp. 147-160, 2024.Wormald, N. C. "A 4-Chromatic Graph With a Special Plane Drawing." 《J. Austral. Math. Soc.》 28, 1-8, 1979.
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