Patents.
4,264,133; 4,264,134; 4,264,148; 4,266,129; 4,266,130; 4,269,485; 4,274,704; 4,274,742; 4,281,930; 4,283,144; 4,284,329; 4,285,577; 4,285,578; 4,286,878; 4,288,163; 4,289,837; 4,290,697; 4,291,109; 4,291,984; 4,293,224; 4,299,229.