Patents.
4,611,915; 4,615,034; 4,617,666; 4,618,957; 4,620,773; 4,621,902; 4,624,569; 4,627,418; 4,628,513; 4,639,069; 4,639,075; 4,639,082; 4,639,092; 4,639,094; 4,641,022; 4,640,580; 4,641,913; 4,641,650; 4,641,914; 4,641,917; 4,641,927; 4,641,931; 4,642,439; 4,643,545; 4,650,275; 4,650,287; 4,650,290; 4,650,292; 4,650,321; 4,652,092; 4,653,870; 4,653,871; 4,653,872; 4,653,873; 4,653,874; 4,653,876; 4,653,877; 4,653,887; 4,655,539; 4,655,540; 4,655,555; 4,657,351; 4,657,352; 4,659,171; 4,659,184; 4,659,186; 4,659,187; 4,659,188; 4,659,189; 4,659,190; 4,660,940; 4,662,723; 4,662,724.