1. See, for example,G. Wanders:Analyticity, unitarity and crossing-symmetry constraints for pion-pion partial-wave amplitudes, Lecture note at Heidelberg-Karlsruhe International Summer Institute in Theoretical Physics, Heidelberg, July 1970.
2. G. Auberson, O. Brander, G. Mahoux andA. Martin:Nuovo Cimento,65 A, 743 (1970) and references mentioned there.
3. G. Auberson:Nuovo Cimento,68 A, 281 (1970).
4. See, for example,J. C. Le Guillou, A. Morel andH. Navelet: CERN preprint TH. 1260 (1970), to be published inNuovo Cimento.
5. J. L. Basdevant, G. Cohen-Tannoudji andA. Morel:Nuovo Cimento,64 A, 585 (1969).