1. H. Goldstein, J. L. Safko, C.P. Poole Jr., Classical Mechanics, 3rd ed., §3.6, Pearson, 2014.
2. J. Bertrand, Théorème relatif au mouvement d’un point attiré vers un centre fixe, C. R. Acad. Sci., Paris 77 (1873), 849-853.
3. I. Newton, The Principia, U. of California Press, 1999; Principia, Dunod, 2011, Prop. VII, Cor. 3; Prop. X, Problem V; Prop. XI, Problem VI.
4. T. Needham, Newton and the transmutation of forces, Am. Math. Mon. 100 (1993), 119-137.
5. C. Mac-Laurin, A Treatise of Fluxions in Two Books, T. W. and T. Ruddimana, Edinburgh, 1742.