Patents.
3,473,030; 3,482,189; 3,487,254; 3,473,031; 3,516,744; 3,521,941; 3,523,735; 3,527,525; 3,528,723; 3,531,179; 3,531,180; 3,531,181; 3,531,184; 3,531,185; 3,531,186; 3,533,015; 3,536,373; 3,536,375; 3,536,832; 3,537,772; 3,537,773; 3,537,774; 3,537,775; 3,539,241; 3,539,246; 3,539,249; 3,539,816.