Patents.
4,807,212; 4,822,120; 4,875,756; 4,875,765; 4,886,331; 4,886,345; 4,886,362; 4,887,885; 4,889,409; 4,889,414; 4,893,887; 4.895,419; 4,898,436; 4,900,133; 4,900,139; 4,900,141; 4,900,918; 4,900,934.