1. Berlekamp, E.R., Gilbert, E.N., Sinden, F.W.: A polygon problem. Am. Math. Mon. 72, 233–241 (1965)
2. Bürgi, J.: Fundamentum Astronomiæ, 1592. Digital Library of the University of Wrocław. http://www.bibliotekacyfrowa.pl/dlibra/doccontent?id=45624 . Accessed: 27 October 2017
3. Chang, G., Davis, P.J.: A circulant formulation of the Napoleon-Douglas-Neumann theorem. Linear Algebra Appl. 54, 87–95 (1983)
4. Science Networks, Historical Studies 53;K Clark,2015
5. Darboux, G.: Sur un problème de géométrie élémentaire, Bull. Sci. Math. Astr. 2e Sér. 2, pp. 298–304 (1878). http://archive.numdam.org/ARCHIVE/BSMA/BSMA_1878_2_2_1/BSMA_1878_2_2_1_298_1/BSMA_1878_2_2_1_298_1.pdf . Accessed: 27 October 2017