1. For a recent account see for instance J. B. French and J. P. Draayer, Proceedings Vllth Int. Coll. on Group Theoretical Methods in Physics, Austin (1978), Lecture Notes in Physics vol. 94 (Springer, Berlin, 1979) p. 394.
2. C. Quesne, J. Math. Phys. 16, 2427 (1975).
3. J. B. French and K. F. Ratcliff, Phys. Rev. C3, 94 (1971).
4. J. B. French, in Nuclear Structure, edited by A. Hossain, Harun-ar-Rashid, and M. Islam ( North-Holland, Amsterdam, 1967 ).
5. F. S. Chang, J. B. French, and T.H. Thio, Ann. Phys. (N.Y.) 66, 137 (1971).