Patents.
5,090,400; 5,090,400; 5,108,172; 5,111,343; 5,113,284; 5,116,121; 5,116,126; 5,119,679; 5,120,128; 5,120,130; 5,120,133; 5,120,961; 5,123,730; 5,129,718; 5,129,724; 5,131,747; 5,136,164; 5,137,348; 5,138,159; 5,141,312; 5,142,403; 5,142,418; 5,144,356; 5,144,477.