1. K. Benko, M. Kothe, K. D. Semmler andU. Simon, Eigenvalues of the Laplacian and Curvature. Colloq. Math.42, 19?31 (1979).
2. B. Y. Chen andC. S. Houh, Totally Real Submanifolds of a Quaternion Projective Space. Ann. Mat. Pura Appl.120, 185?199 (1979).
3. S. S.Chern, M.do Carmo and S.Kobayashi, Minimal Submanifolds of a Sphere with Second Fundamental Form of Constant Length. Shiing-shen Chern Selected Papers, 393?409, Berlin-Heidelberg-New York 1978.
4. Y. B. Shen, On Intrinsic Rigidity for Minimal Submaifolds in a Sphere. Scie. China (Ser. A),32, 769?781 (1989).
5. Y. B. Shen, Totally Real Minimal Submanifolds in a Quaternion Projective Space. Preprint, Hangzhou University, China 1988.