Patents.
3,888,569; 3,889,226; 3,914,544; 3,915,548; 3,915,549; 3,915,551; 3,917,378; 3,917,379; 3,917,380; 3,936,138; 3,936,139; 3,938,896; 3,942,008; 3,942,861; 3,947,084; 3,947,086; 3,951,524; 3,953,106; 3,953,667; 3,953,863; 3,958,104; 3,958,865; 3,961,838; 3,961,846.