1. Halphen, M.: Sure les invariants différentiels des courbes gauches. J. Éc. Polytech. 28(1) (1880)
2. Wilczynski, E.J.: Projective Differential Geometry of Curves and Ruled Surfaces. Teubner, Leipzig (1906)
3. Wilczynski, E.J.: Projective differential geometry of curved surface (second memoir). Trans. Am. Math. Soc. 9(1), 79–120 (1908)
4. Čech, E., Fubini, G.: Geometria Proiettiva Differenziale. Zanichelli, Bologna (1927)
5. Weyl, H.: The Classical Group. Princeton University Press, Princeton (1939)