Patents.
3,432,239; 3,434,771; 3,436,153; 3,437,825; 3,438,694; 3,442,594; 3,457,414; 3,463,574; 3,463,882; 3,461,295; 3,462,211; 3,462,212; 3,462,213; 3,462,603; 3,462,604; 3,462,712; 3,463,142; 3,463,572; 3,463,593; 3,463,915; 3,463,926; 3,464,760; 3,464,762; 3,461,298; 3,467,463; 3,468,609; 3,471,240; 3,473,013; 3,469,030; 3,469,206; 3,469,923; 3,471,212.