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2. S. Hatakawa:Phys. Rev.,108, 1533 (1957);G. W. Clark andJ. Hersil:Phys. Rev.,108, 1538 (1957). We are grateful to Professor Clark for communicating the M.I.T. results to us before publication.
3. R. Levi-Setti, R. Garwin, A. Alihanian, and others:Proceedings of the Padua-Venice Conference (1957) (mimeographed edition).
4. G. Culligan, S. C. P. Frank, J. R. Holt, J. C. Kluyver andT. Massam:Naiure,180, 751 (1957);T. D. Lee:Midwest Conference on Theoretical Physics, St. Louis (1958) (unpublished)).
5. H. A. Tolhoek:Rev. Mod. Pliys.,28, 277 (1956).