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3. F.H. Shepard, Jr., U.S. Patent No. 2,333,688 (November 9, 1943).
4. W.E. Kock, U.S. Patent No. 2,400,309 (May 14, 1946).
5. M.J. Larsen, U.S. Patent No. 2,580,560 (January 1, 1952).