Patents.
4,805,986; 4,807,997; 4,815,804; 4,815,805; 4,818,108; 4,828,368; 4,828,371; 4,830,441; 4,830,442; 4,830,449; 4,834,474; 4,834,476; 4,834,473; 4,834,513; 4,835,380; 4,835,732; 4,836,630; 4,836,646; 4,836,664; 4,836,673; 4,838,687; 4,840,465.