Patents.
4,647,154; 4,697,881; 4,701,020; 4,701,940; 4,705,343; 4,712,916; 4,716,287; 4,717,220; 4,718,417; 4,719,344; 4,721,369; 4,721,379; 4,722,596; 4,723,077; 4,723,438; 4,723,448; 4,723,829; 4,723,836; 4,724,329; 4,725,110; 4,725,113; 4,725,124; 4,726,639; 4,729,240; 4,729,634; 4,729,640; 4,729,655; 4,730,113; 4,732,482.