Patents.
3,508,812; 3,510,201; 3,511,557; 3,511,558; 3,512,872; 3,512,874; 3,514,185; 3,514,189; 3,515,462; 3,515,463; 3,516,735; 3,517,979; 3,517,984; 3,517,985; 3,517,986; 3,517,987; 3,519,333; 3,527,520; 3,528,725; 3,528,726; 3,529,148; 3,531,304; 3,531,305; 3,531,306; 3,533,340; 3,533,682; 3,538,321; 3,539,263;