Patents.
4,685,777; 4,725,109; 4,725,138; 4,728,185; 4,729,622; 4,729,658; 4,730,882; 4,733,955; 4,733,967; 4,735,487; 4,735,489; 4,735,493; 4,735,496; 4,736,360; 4,738,499; 4,738,501; 4,738,503; 4,740,082.