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2. A. P. Balachandran andJ. Nuyts:Phys. Rev.,172, 1821 (1968).
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4. G. F. Chew andS. Mandelstam:Phys. Rev.,119, 467 (1960).
5. See, for example,Higher Transcendental Functions, Bateman Manuscript Project, edited byA. Erdelyi, vol.2 (New York, 1953).