Patents.
3,889,207; 3,934,212; 3,937,554; 3,937,555; 3,938,058; 3,941,450; 3,946,332; 3,952,264; 3,957,339; 3,958,188; 3,958,881; 3,976,365; 3,977,772; 3,982,204; 3,982,817; 3,982,821; 3,982,822; 3,982,823; 3,982,824; 3,983,509; 3,983,510; 3,983,511; 3,984,155; 3,989,317; 3,990,785;