Patents.
3,963,347; 3,963,995; 3,964,003; 3,965,439; 3,965,440; 3,967,211; 3,967,212; 3,968,456; 3,969,687; 3,969,688; 3,992,085; 3,992,086; 3,994,574; 3,994,575; 3,997,247; 3,998,527; 3,999,840; 4,009,943; 4,009,944; 4,012,126; 4,013,349; 4,013,350; 4,018,511.