1. Erbacher, J.: Isometric immersions of riemannian manifolds into space forms. Ph. D. Thesis. Brown University 1970. Providence, R. I.
2. Eisenhart, L.P.: A treatise on the differential geometry of curves and surfaces. New York: Dover 1960.
3. Hopf, H.: Lectures on differential geometry in the large. Mimeographed notes. Stanford University, California.
4. Kobayashi, S., Nomizu, K.: Foundations of differential geometry. I. New York-London: Interscience Publ. 1963.
5. Ōtsuki, T.: A theory of riemannian submanifolds. Kōdai Math. Sem. Rep.20, 282–295 (1968).