Patents.
4,798,446; 4,856,861; 4,856,880; 4,856,897; 4,856,899; 4,857,425; 4,859,013; 4,863,224; 4,865,406; 4,865,429; 4,871,254; 4,874,213; 4,874,214; 4,863,225; 4,874,244; 4,880,298; 4,880,304; 4,880,991; 4,884,879; 4,886,341.