1. (a) NCR Corp., British Pat. 1,109,554 (1968);
2. (b) W. J. Becker and P. L. Foris, U.S. Pat. 3,364,023 (1968);
3. (c) NCR Corp., British Pat. 1,073,999 (1976);
4. (d) W. J. Becker and P. L. Foris, U.S. Pat. 3,359, 103 (1967).
5. E. Berman and H. Schwab, U.S. Pat. 3,072, 481 (1963).