Patents.
4,812,028; 4,853,933; 4,858,238; 4,867,536; 4,874,220; 4,880,299; 4,880,965; 4,883,348; 4,887,886; 4,887,890; 4,890,901; 4,900,111; 4,900,138; 4,902,105; 4,904,039; 4,904,070; 4,906,077; 4,907,865; 4,907,866; 4,908,054; 4,907,872; 4,913,535.