Patents.
4,142,773; 4,126,392 4,151,411; 4,168,437; 4,168,696; 4,168,716; 4,170,985; 4,171,695; 4,189,214; 4,190,321; 4,190,366; 4,191,470; 4,191,474; 4,191,477; 4,192,577; 4,192,994; 4,192,995; 4,193,667; 4,193,693; 4,194,813; 4,194,815; 4,195,311; 4,195,914; 4,196,967; 4,196,968; 4,196,969; 4,196,970; 4,198,126; 4,198,127; 4,198,128; 4,198,129.