Patents.
3,967,884; 3,973,831; 3,973,833; 3,981,577; 3,989,360; 3,994,572; 4,132,463; 4,135,786; 4,141,636; 4,142,779; 4,145,108; 4,145,116; 4,145,117; 4,146,304; 4,147,410; 4,151,654; 4,153,370; 4,156,137; 4,160,159; 4,160,263; 4,160,269; 4,161,347; 4,161,348; 4,161,656; 4,162,118; 4,162,124; 4,163,542; 4,165,178; 4,165,183; 4,167,677; 4,168,116; 4,168,884; 4,168,900; 4,171,870; 4,176,925; 4,176,950; 4,176,960; 4,178,511; 4,191,452; 4,191,454; 4,193,687; 4,197,010; 4,198,115.