1. R. Arvieu: Thesis, University of Paris (1963), unpublished;
2. P. L. Ottaviani, M. Savoia, J. Sawicki andA. Tomasini:Phys. Rev.,153, 1138 (1967);
3. M. K. Pal andY. K. Gambhir:Phys. Rev.,155, 1144 (1967);163, 1004 (1967).
4. M. Baranger:Phys. Rev.,120, 957 (1960).
5. M. H. Macfarlane:Lectures in Theoretical Physics (Boulder, Col., 1966), p. 583.