Patents.
4,438,330; 4,439,012; 4,440,498; 4,441,019; 4,444,502; 4,445,050; 4,445,780; 4,447,117; 4,447,124; 4,447,125; 4,447,127; 4,447,130; 4,449,824; 4,451,116; 4,451,118; 4,451,119; 4,451,123; 4,451,148; 4,453,800; 4,455,088; 4,456,329; 4,456,340; 4,456,341; 4,456,343; 4,456,345; 4,457,590; 4,457,592; 4,457,595; 4,457,596; 4,458,147; 4,460,250; 4,460,828; 4,461,543;