Singularities in the physical region

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J. B. Bronzan:Phys. Rev.,134, B 687 (1964); B. E. Norton:Phys. Rev.,135, B 1381 (1964); C. Kacser:Phys. Lett.,12, 269 (1964); I. J. E. AitchiSOn:Phys. Rev.,133, B 1257 (1964).

E. F. PeierlS:Phys. Rev. Lett.,6, 641 (1961); C. Goebel:Phys. Rev. Lett.,13, 143 (1964); E. C. Hwa:Phys. Rev.,130, 1580 (1963).

R. J. Eden:Phys. Rev.,119, 1763 (1960).

R. J. Eden, P. V. Landshoff, J. C. Polkinghorne andJ. C. Taylor:Journ. Math. Phys.,2, 656 (1961).