1. I. Ia. Pomeranchuk:Žurn. Ėksp. Teor. Fiz.,30, 423 (1956) (translation:Sov. Phys. JETP,3, 306 (1956));L. B. Okun andI. Ia. Pomeranchuk:Žurn. Ėksp. Teor. Fiz.,30, 424 (1956) (translation:Sov. Phys. JETP.3, 307 (1956)).
2. D. Amati, L. L. Foldy, A. Stanghellini andL. Van Hove:Nuovo Cimento,32, 1685 (1964);L. L. Foldy andR. F. Peierls:Phys. Rev.,130, 1585 (1963);D. Amati, S. Fubini andA. Stanghellini:Nuovo Cimento,26, 896 (1962).
3. S. Meshkov andG. B. Yodh:Phys. Rev. Lett.,19, 603 (1967).
4. For a recent review seeH. Harari:XIV International Conference on High Energy Physics (Vienna, 1968); or SLAC-PUB-508 (1968).
5. H. Harari:Phys. Rev. Lett.,20, 1395 (1968);P. G. O. Freund: Eurico Fermi Institute preprint, No. EFI. 68–85 (1968).