Patents.
4,630,097; 4,639,586; 4,645,346; 4,645,314; 4,649,273; 4,650,286; 4,650,284; 4,650,315; 4,665,541; 4,666,261; 4,666,298; 4,669,815; 4,669,831; 4,671,620; 4,671,621; 4,671,626; 4,671,627; 4,671,628; 4,672,192; 4,673,241; 4,673,258; 4,673,259; 4,676,607.