1. ADAMAS P.J., U.S. Patent (7.1.67), n? 789 607
2. GETSON J.C., U.S. Patent (8.13.69), n? 849 920
3. GETSON J.C., Brevet Français (4.8.69), n? 1 567 098
4. NEUROTH C.G., U.S. Patent (2.23.71), n? 3 565 851
5. LINDSEY S.E., U.S. Patent (5.1.72), n? 249 327