Patents.
4,265,510; 4,268,800; 4,269,481; 4,269,511; 4,271,397; 4,272,158; 4,272,159; 4,272,194; 4,273,444; 4,273,445; 4,277,129; 4,277,760; 4,278,330; 4,278,351; 4,280,109; 4,280,751; 4,280,764; 4,280,766; 4,281,893; 4,281,904; 4,281,905; 4,281,906; 4,281,908; 4,282,431; 4,283,122; 4,283,123; 4,284,323; 4,284,885; 4,285,570; 4,285,579; 4,285,596; 4,286,844; 4,286,848; 4,287,421; 4,289,372; 4,289,385;