1. K. O. Friedrichs, Los Alamos Report No. 2105 (written 1954, distributed 1957).
2. See also K. O. Friedrichs and H. Kranzer, NYO-6486-VIII, Institute of Mathematical Sciences, New York University (1958).
3. Propagation of Weak Hydromagnetic Discontinuities
4. Green's Function for Two-Dimensional Magnetohydrodynamic Waves. I
5. H. Dorrie,Hubische u. Biquadratische Gleichungen(Leibniz Verlag, München, 1948), pp. 59.