Patents.
5,011,254; 5,040,872; 5,052,780; 5,066,127; 5,067,801; 5,069,548; 5,069,551; 5,071,207; 5,070,874; 5,071,209; 5,071,239; 5,072,104; 5,073,007; 5,073,016; 5,073,108; 5,074,629; 5,073,705; 5,074,645; 5,076,655.