Patent.
3,663,084; 3,666,347; 3,667,827; 3,669,530; 3,679,294; 3,711,192; 3,713,740; 3,722,982; 3,737,214; 3,748,021; 3,749,489; 3,752,591; 3,740,120; 3,741,630; 3,743,385; 3,743,387; 3,746,428; 3,748,015; 3,748,020; 3,756,697; 3,761,157; 3,761,158; 3,762,801; 3,764,209; 3,783,764; 3,783,765; 3,784,277; 3,788,735; 3,788,749; 3,790,256; 3,790,257; 3,791,713; 3,814,496; 3,814,504; 3,815,974; 3,817,603; 3,823,999; 3,826,911; 3,827,059; 3,827,778; 3,827,785; 3,832,035; 3,832,037; 3,833,283; 3,845,308;