1. Anzer, U. and Tandberg-Hanssen, E.: 1970, Solar Phys. 11, 61.
2. Barnes, C. W. and Sturrock, P. A.: 1972, Astrophys. J. 174, 659.
3. Bruzek, A.: 1963, in W. N. Hess (ed.), AAS-NASA Symposium on the Physics of Solar Flares, NASA SP-50, p. 301.
4. Courant, R. and Hilbert, D.: 1962, Methods of Mathematical Physics, Vol. II by R. Courant, Interscience, New York, London.
5. Gold, T.: 1963, in W. N. Hess (ed.), AAS-NASA Symposium on the Physics of Solar Flares, NASA SP-50, p. 389.