1. W.W. Kaeding, R.O. Lindblom and R.G. Temple, US Patent 2 727 926 (20 Dec. 1955).
2. R.D. Barnard, Walnut Creek and R.H. Meyer, US Patent 2 852 567 (16 Sept 1958).
3. C.T. Lam and D.M. Shannon, US Patent 4 567 157 (28 Jan. 1986).
4. D.F. Pontz, US Patent 3 288 865 (29 Nov. 1966).
5. R.E. Woodward, US Patent 3 356 744 (5 Dec. 1967).