Patents.
3,711,181; 3,818,373; 3,854,044; 3,858,965; 3,858,977; 3,868,175; 3,919,662; 3,926,504; 3,928,814; 3,919,664; 3,928,816; 3,928,820; 3,928,821; 3,931,592; 3,936,147; 3,931,589; 3,936,152; 3,937,562; 3,938,883; 3,941,452; 3,942,874; 3,942,875; 3,942,876; 3,942,877.