Patents.
3,702,722; 3,704,935; 3,709,605; 3,709,693; 3,713,823; 3,719,773; 3,721,491; 3,721,557; 3,726,593; 3,728,006; 3,736,145; 3,738,731; 3,739,088; 3,743,768; 3,747,755; 3,748,014; 3,748,041; 3,756,702; 3,758,201; 3,760,181; 3,761,714; 3,761,715; 3,761,160; 3,762,803.