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Heule Spindle
The Heule spindle is the 10-node unit-distance graph illustrated above (Soifer 2024, pp. 696-697) with chromatic number 4. It can be used to construct unit-distance graphs having chromatic number 5 without the use of Moser spindles. It appears as a subgraph in the de Grey graph, Exoo-Ismailescu graphs on 49, 51, and 627 nodes, Heule graphs, Mixon graphs, and Parts graphs on 510, 525, 529, and 553 vertices. It also appears in the 51-braced dodecagon, 45-braced octagon, 75-braced pentagon, and 21-braced square.
Unlike the Moser spindle, it is a matchstick graph. It is illustrated above in a number of embeddings.
It is implemented in the Wolfram Language as GraphData["HeuleSpindle"].
See also
de Grey Graphs, Heule Graphs, Moser SpindleExplore with Wolfram|Alpha
References
House of Graphs. "Graph 20767." https://houseofgraphs.org/graphs/20767.Soifer, A. The New Mathematical Coloring Book: Mathematics of Coloring and the Colorful Life of Its Creators, 2nd ed. New York: Springer, 2024.Referenced on Wolfram|Alpha
Heule SpindleCite this as:
Weisstein, Eric W. "Heule Spindle." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/HeuleSpindle.html