1. Yu. N. Demkov and V. N. Ostrovskii, Method of Zero-Range Potentials in Atomic Physics [in Russian], Izd-Vo LGU (1975).
2. G. Breit, Ann. Phys.,34, 377 (1965); G. H. Herling and Y. Nishida, Ann. Phys.,34, 400 (1965). Y. Nishida, Ann. Phys.,34, 415 (1965).
3. S. K. Zhdanov and A. S. Chikhachev, Dokl. Akad. Nauk SSSR,218, 1323 (1974).
4. Yu. N. Demkov and V. I. Osherov, Zh. Eksp. Teor. Fiz.,53, 1589 (1967).
5. Yu. N. Demkov, Zh. Eksp. Teor. Fiz.,45, 197 (1963).