1. M. Gell-Mann, R. S. Oakes andB. Renner:Phys. Rev.,175, 2196 (1968).
2. M. Ademollo andR. Gatto:Nuovo Cimento,44 A, 282 (1966).
3. J. Ellis:Nucl. Phys.,13 B, 153 (1969).
4. Actually in ref. (1,3),β is assumed to be a smooth function not only int but also in the mass variables betweent=0 andt=m 2 K .
5. This statement becomes trivial in theSU 2 ⊗SU 2 limit, if we assume that this limit is realized by massless pions.