Patents.
4,165,464; 4,164,650; 4,167,335; 4,168,427; 4,174,634; 4,178,510; 4,174,885; 4,175,365; 4,182,549; 4,183,624; 4,183,625; 4,183,626; 4,184,749; 4,183,668; 4,183,780; 4,184,700; 4,185,885; 4,185,891.