1. Klein, A., Rafelski, J.: Phys. Rev. D11, 300 (1975)
2. Bawin, M., Lavine, J. P.: Phys. Rev. D12, 1192 (1975)
3. Klein, A., Rafelski, J.: Phys. Rev. D12, 1194 (1975)
4. It should also be emphasized that only this case was studied by A.B. Migdal, Zh. Eksp. Teor. Fiz.61, 2209 (1971) [Sov. Phys.-JETP34, 1184 (1972)], the publication which stimulated much of the interest in pion condensation
5. Zel'dovich, Ya.B., Popov, V.S.: Usp. Fiz. Nauk105, 403 (1971). [Sov. Phys.-Usp.14, 673 (1972)]