Patents.
4,778,249; 4,782,209; 4,796,971; 4,796,976; 4,815,807; 4,815,829; 4,815,830; 4,815,849; 4,818,079; 4,818,081; 4,818,082; 4,822,124; 4,824,192; 4,824,224; 4,824,236; 4,826,283; 4,826,299; 4,826,301.