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2. L. K. Pandit:Helv. Phys. Acta,31, 379 (1958);Nuovo Cimento,10, 534 (1958).
3. L. O’Raifeartaigh, B. Sredniava andCh. Tereaux: to be published.
4. E. Arnous andW. Heitler:Nuovo Cimento,2, 1282 (1955).
5. C. Møller andP. Kristensen:Kong. Dansk. Vid. Selsk.,27, no. 7 (1952).