1. Cfr.The Derived Directions of a Vector defined along a Curve in Riemannian Space. Proc. Lond. Math. Soc., (2). 28, (1928), 501–509.
2. Levi-Civita,The Absolute Differential Calculus, (1927), p. 275.
3. Levi-Civita, loc. cit., p. 275.
4. Eisenhart,Riemannian Geometry, (1926), pp. 234–235.
5. Eisenhart, loc. cit., pp. 233–234.