1. Allen, A. J. and Hughes, P. A.: 1984,Monthly Notices Roy. Astron. Soc. 208, 609.
2. Bellman, R. and Pennington, R. H.: 1954,Appl. Math. 12, 151.
3. Bhatia, P. K. and Chhonkar, R. P. S.: 1985,Astrophys. Space Sci. 114, 271.
4. Chandrasekhar, S.: 1961,Hydrodynamic and Hydromagnetic Stability, Clarendon Press, Oxford, Chapter X.
5. Craik, A. D. D.: 1976,Phys. Fluids 19, 479.