Patents.
4,470,661; 4,523,806; 4,523,813; 4,523,814; 4,523,816; 4,523,817; 4,523,846; 4,525,024; 4,525,035; 4,525,036; 4,525,038; 4,525,040; 4,526,442; 4,526,443; 4,527,864; 4,527,866; 4,527,867; 4,527,868; 4,530,564; 4,530,565; 4,530,575; 4,531,815; 4,531,835; 4,532,422; 4,537,476; 4,533,207; 4,533,208; 4,533,211; 4,533,828; 4,534,626; 4,536,086; 4,537,464; 4,537,472; 4,540,248; 4,540,249.