Patents.
4,834,508; 4,840,459; 4,840,462; 4,848,885; 4,859,042; 4,859,044; 4,861,145; 4,861,146; 4,861,148; 4,861,163; 4,861,164; 4,863,250; 4,863,251; 4,861,975; 4,861,981; 4,863,252; 4,864,137; 4,783,385; 4,864,869.