Patents.
4,824,214; 4,824,217; 4,826,293; ,4,832,464; 4,838,247; 4,848,894; 4,850,365; 4,851,696; 4,854,662; 4,854,677; 4,854,681; 4,854,683; 4,854,686; 4,856,857; 4,856,858; 4,856,889; 4,856,860; 4,859,011; 4,859,028; 4,859,861.