1. F. Klein:Geometry (New York, 1939).
2. F. Klein:Gesammelte Werke, I (Berlin, 1921).
3. R. Hermann:Lie Groups for Physicists (New York, 1966).
4. H. A. Kastrup:Nucl. Phys.,58, 561 (1964).
5. G. W. Mackey:Mathematical Foundations of Quantum Mechanics (New York, 1963).