Patents.
4,204,881; 4,338,516; 4,342,917; 4,340,271; 4,343,874; 4,342,503; 4,344,691; 4,345,815; 4,436,292; 4,346,293; 4,348,081; 4,348,082; 4,346,962; 4,348,084; 4,348,085; 4,348,090; 4,350,411; 4,350,412.