Patents.
5,117,349; 5,193,015; 5,193,025; 5,210,398; 5,212,536; 5,233,454; 5,233,554; 5,235,177; 5,235,183; 5,235,438; 5,237,160; 5,237,452; 5,243,458; 5,245,472; 5,247,176; 5,249,081; 5,251,007; 5,253,088; 5,260,767.