1. K. O. Friedrichs, “Nonlinear wave motion in magneto-hydrodynamics,” Los Alamos Report No. 2105 (written 1954, distributed 1957).
2. See also a later version of this work by K. O. Friedrichs and H. Kranzer, Report No. MH-8, AEC Computing and Applied Math. Center, Inst. of Math. Sci., New York University, New York (1958).
3. See, for example, the lecture notes by R. K. Luneberg, “Mathematical theory of optics,” Brown University (1944);
4. “Propagation of electromagnetic waves,” New York University, New York (1949).