Patents.
3,669,528; 3,687,518; 3,697,150; 3,698,795; 3,703,641; 3,706,485; 3,709,582; 3,710,696; 3,711,184; 3,711,185; 3,711,186; 3,711,199; 3,711,713; 3,711,723; 3,711,791; 3,712,724; 3,712,709; 3,712,711; 3,715,685; 3,718,380; 3,718,383; 3,718,398; 3,719,409; 3,719,420; 3,719,823; 3,720,456; 3,720,884; 3,721,828; 3,721,915; 3,721,916; ; 3,724,933; 3,725,815.