1. G. Veneziano:Nuovo Cimento,57 A, 190 (1968).
2. C. Schmid:Construction of the ππ scattering amplitude from superconvergence, CERN, TH 956.
3. S. Mandelstam:Phys. Rev. Lett.,21, 1724 (1968).
4. See for instanceA. Erdelyi, W. Magnus, F. Oberhettinger andF. G. Tricomi:Higher Transcendental Functions, vol.1, 13.
5. See ref. (4), instanceA. Erdelyi, W. Magnus, F. Oberhettinger andF. G. Tricomi:Higher Transcendental Functions, vol.1, 1.10.