1. Barcza, S.: 1968, Ph.D. Thesis, Lorand Eötvös University, Budapest.
2. Bohm, D. and Pines, D.: 1953,Phys. Rev. 92, 609;92, 626.
3. Bridgman, P. W.: 1963,Solids Under Pressure, McGraw-Hill Book Co., New York, ch. 1.
4. Cooper, J.: 1966,Reports on Progress in Physics 29, Part 1, p. 35.
5. Stars and Stellar Systems;A. N. Cox,1965