1. D. E. Baldwin, I. B. Bernstein, and M. P. H. Weenink, inAdvances in Plasma Physics, edited by A. Simon and W. B. Thompson (Interscience, New York, 1969), Vol. III, p. 1.
2. Asymptotic theory of wave-propagation
3. Kinematic wave theory
4. R. Courant and D. Hilbert,Methods of Mathematical Physics(Interscience, New York, 1966), Vol. I, Chap. I.
5. T. H. Stix,The Theory of Plasma Waves(McGraw-Hill, New York, 1962), p. 48.