Patents.
3,782,806; 3,802,778; 3,803,407; 3,804,521; 3,806,224; 3,807,832; 3,808,422; 3,811,096; 3,813,544; 3,849,742; 3,851,951; 3,852,683; 3,852,684; 3,855,546; 3,855,547; 3,856,403; 3,857,109; 3,857,636; 3,860,343; 3,860,884; 3,860,888; 3,865,975; 3,868,169; 3,871,739; 3,872,400; 3,869,210; 3,872,402; 3,872,403; 3,872,407; 3,876,829; 3,880,522; 3,880,523; 3,883,688.