1. H. R. Lewis, Jr., Phys. Rev. Lett. 18, 510–12 (1967); PRLTAO0031-9007
2. H. R. Lewis, Jr., J. Math. Phys. 9, 1976–86 (1968).JMAPAQ0022-2488
3. B. Leaf, J. Math. Phys. 10, 1971–79 (1969); JMAPAQ0022-2488
4. B. Leaf, J. Math. Phys. 10, 1980–87 (1969); JMAPAQ0022-2488
5. M. Moshinsky, J. Math. Phys. 12, 1772–83 (1971).JMAPAQ0022-2488