Patents.
3,741,658; 3,767,284; 3,806,897; 3,817,634; 3,829,684; 3,831,165; 3,831,165; 3,832,034; 3,834,791; 3,877,776; 3,883,215; 3,883,216; 3,891,968; 3,891,975; 3,938,879; 3,939,345; 3,942,007; 3,942,871; 3,944,329; 3,944,335; 3,949,162; 3,960,441.