1. W. A. Bardeen andB. W. Lee: inNuclear and Particle Physics, edited byB. Margolis andC. S. Lam (New York, 1968).
2. S. Weinberg:Phys. Rev.,166, 1568 (1968).
3. A special case has been considered byW. Sollfrey:Phys. Rev.,173, 1805 (1968).
4. We have recently become aware of a different form obtained byS. P. Rosen, which is also independent of the definition of the pion field;The relationship between nonlinear and linear realizations of chiral SU2 × SU2,Purdue University preprint (1970).
5. J. Schwinger:Phys. Rev.,167, 1432 (1968).