1. For example, Proceedings 1958, 1959, 1962 Conferences on High Energy Physics; 1961 Aix-en-Provence Conference.
2. Goldstone, Salam, and Weinberg, Phys. Rev. 127, 965 (1962).
3. Gell-Mann and Low, Phys. Rev. 95, 300 (1954).
4. Källen and Wightman, Kgl. Danske Vid. Selsk. Mat-Phys. Skr. 1, 6 (1958). Källen and Toll,
5. Andreassi, Budini, and Furlan, Phys. Rev. Letters 8, 184 (1962).