Patents.
4,080,048; 4,081,210; 4,083,628; 4,084,885; 4,089,591; 4,093,348; 4,094,588; 4,095,873; 4,099,843; 4,099,849 4,099,850; 4,101,203; 4,101,204; 4,110,777; 4,117,328; 4,117,329; 4,122,466; 4,118,722; 4,122,344; 4,127,318.