1. R. Ambrose, W.-H. Chang, D. Mckeough, J. Peffer, US 4,543,405 (1985).
2. G. Parekh, W. Blank, US 4,631,320 (1986).
3. J. Gardon, S. Loper, P. Uhlianuk, F. Walker, US 5,155,201 (1992).
4. F. Walker, J. Gardon, US 5,130,405 (1992).
5. J. Gardon, P. Uhlianuk, S. Loper, US 5,175,227 (1992).