1. Massau, J., Mem. sur l’integration graphique des equations aux derivees partielles, Gand 1900–03; cf. also Enzykl. d. Math Wiss. 2, 31, p. 159.
2. Meyer, R. E., The method of characteristics for problems of compressible flow involving two independent variables,Part I, General Theory, Quart. J. Mech. App’. Math. 1, pt 2, June 1948.
3. Tollmien, W., Steady two-dimensional and axially symmetrical supersonic flows, Brown Univ. Translation No. A9-T-1, 1948.
4. Courant, R., and Friedrichs, K. O., Supersonic Flow and Shock Waves, Interscience Publishers, Inc., New York, 1948.
5. Courant, R., and Hilbert, D., Methoden der Mathenntischen Physik II, chapter 5, Verlag von Julius Springer, Berlin 1937.