Patents.
3,704,937; 3,709,610; 3,712,813; 3,713,032; 3,715,164; 3,717,412; 3,717,415; 3,725,812; 3,725,814; 3,725,817; 3,729,690; 3,729,704; 3,736,040; 3,737,212; 3,737,231; 3,737,629; 3,743,422; 3,748,753; 3,751,132; 3,764,978; 3,786,367.