Patents.
3,712,716; 3,716,666; 3,718,389; 3,718,752; 3,719,127; 3,721,486; 3,721,487; 3,722,986; 3,724,932; 3,726,587; 3,726,598; 3,728,010; 3,728,011; 3,729,249; 3,729,261; 3,731,231; 3,731,989; 3,731,990; 3,732,412; 3,733,115; 3,734,600; 3,736,048; 3,736,049.