The Moser spindle is the 7-node unit-distance graph illustrated above (Read and Wilson 1998, p. 187). It is sometimes
called the Hajós graph (e.g., Bondy and Murty
2008. p. 358), though this term is perhaps more commonly applied to the Sierpiński
gasket graph .
It is a quasi-cubic graph.
Bondy, J. A. and Murty, U. S. R. Graph Theory. Berlin: Springer-Verlag, 2008.de Grey, A. D. N. J.
"The Chromatic Number of the Plane Is at Least 5." Geombinatorics28,
No. 1, 18-31, 2018.Moser, L. and Moser, W. "Problem 10."
Canad. Math. Bull.4, 187-189, 1961.Read, R. C. and
Wilson, R. J. An
Atlas of Graphs. Oxford, England: Oxford University Press, 1998.Soifer,
A. "The Hadwiger-Nelson Problem." In Open
Problems in Mathematics (Ed. J. F. Nash, Jr. and M. Th. Rassias).
Switzerland: Springer, p. 442, 2016.Soifer, A. The
Mathematical Coloring Book: Mathematics of Coloring and the Colorful Life of Its
Creators. New York: Springer, 2008.