Patents.
3,830,558; 3,861,781; 3,861,783; 3,864,018; 3,864,019; 3,874,770; 3,876,290; 3,876,292; 3,877,783; 3,879,105; 3,883,752; 3,884,555; 3,884,556; 3,884,557; 3,885,862; 3,887,262; 3,887,263; 3,887,264; 3,887,269; 3,889,282; 3,891,302; 3,891,304; 3,891,310.