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2. https://alchetron.com/Robert-Willis-(engineer)-1123803-W . Accessed 02 Sept 2017
3. LNCS Homepage. http://www.euler-2007.ch/doc/EulerLec.pdf . Accessed 02 Sept 2017
4. http://en.wikipedia.org/wiki/Involute_gear . Accessed 02 Sept 2017
5. Bogolyubov, N.N., Mikhailov, G.K., Yushkevich, A.P. (eds.): Euler and Modern Science, MAA Spectrum, Mathematical Association of America, Washington, D.C., translated from the Russian by Robert Burns (2007)