Patents.
3,619,021; 3,628,849; 3,644,014; 3,647,278; 3,663,089; 3,659,927; 3,661,441; 3,661,442; 3,682,532; 3,675,986; 3,675,989; 3,713,721; 3,718,078; 3,718,751; 3,719,415; 3,728,545; 3,729,253; 3,734,619; 3,783,295; 3,792,916; 3,793,518; 3,795,803; 3,796,479; 3,797,911; 3,797,913; 3,798,366; 3,798,452; 3,800,156; 3,801,185.