Patents.
5,090,016; 5,090,019; 5,103,452; 5,116,133; 5,117,436; 5,118,922; 5,119,383; 5,121,400; 5,140,598; 5,151,817; 5,151,965; 5,159,601; 5,159,602; 5,159,603; 5,163,058; 5,166,818; 5,166,821; 5,175,736; 5,181,078; 5,185,750; 5,187,759; 5,194,917; 5,202,741; 5,206,922; 5,208,652; 5,208,695; 5,210,637; 5,212,698; 5,216,232; 5,216,739; 5,218,469; 5,223,911; 5,226,049; 5,239,186; 5,239,366.