Patents.
4,269,505; 4,270,837; 4,304,458; 4,305,660; 4,311,357; 4,311,360; 4,314,739; 4,314,743; 4,315,224; 4,315,269; 4,315,669; 4,316,653; 4,316,665; 4,317,042; 4,318,591; 4,318,592; 4,319,809; 4,319,810; 4,320,974.