1. J. Goldstone, A. Salam and S. Weinberg, Phys. Rev. 127, 965 (1962);
2. D. Kastler, D.W. Robinson and J.A. Swieca, Comm. Math. Phys2, 108 (1966);
3. D. Kastler, Broken Symmetries and the Goldstone Theorem in Axiomatic Field theory, in Proceedings of the 1967 International Conference on Particles and Fields, C.R. Hagen et al. eds., Interscience 1967; J.A. Swieca, Goldstone theorem and related topics, in Carg??se Lectures in Physics, Vol. 4, D. Kastler ed., Gordon and Breach 1970; R.F. Streater, Spontaneously broken symmetries, in Many degrees of freedom in Field Theory, L. Streit ed., Plenum Press 1978.
4. The non-relativistic version has been discussed in particular by R.V. Lange, Phys. Rev. Lett. 14, 3 (1965);
5. Phys. Rev. 146, 301 (1966) and by J.A. Swieca, Comm. Math. Phys. 4, 1 (1967).