Patents.
5,000,566; 5,004,310; 5,007,721; 5,134,882; 5,155,553; 5,159,656; 5,137,353; 5,166,813; 5,168,386; 5,170,049; 5,171,994; 5,172,000; 5,172,257; 5,173,598; 5,175,647; 5,175,755; 5,181,012; 5,181,224; 5,182,659; 5,185,647; 5,187,358; 5,187,359; 5,187,360; 5,192,980; 5,198,659; 5,200,861.