1. Resoluzione del problema: riportari i punti di una superficie sopra un piano in modo che le linee geodetische vengano rappresentante da linee rette;Beltrami;Ann. Mat.,1865
2. S. Benenti, Orthogonal separable dynamical systems, in: Differential Geometry and its Applications (Opava, 1992), Math. Publ. 1, Silesian University Opava, Opava, 1993, pp. 163–184.
3. S. Benenti, Inertia tensors and Stäckel systems in the Euclidean spaces, in: Differential Geometry (Turin, 1992), Vol. 50, No. 4, Rend. Sem. Mat. Univ. Politec., Torino, 1992, pp. 315–341.
4. A completely integrable mechanical system;Braden;Lett. Math. Phys.,1982
5. L.P. Eisenhart, Riemannian Geometry, 2nd Edition, Princeton University Press, Princeton, NJ, 1949.