1. Ladyzhenskii, M.D., Prostranstvennye giperzvukovye techeniya gaza (Spatial Hypersonic Gas Flows), Moscow: Mashinostroenie, 1968.
2. Shifrin, E.G., On the extremal properties of entropy on a critical streamline, J. Appl. Math. Mech., 1967, vol. 31, no. 3, pp. 618–620.
3. Batchelor, G.K., An Introduction to Fluid Dynamics, CUP, 1970.
4. Von Mises, R., Mathematical Theory of Compressible Fluid Flow, New York: Academic, 1958.
5. Prim, R. and Truesdell, C., A derivation of Zorawski’s criterion for permanent vector-lines, Proc. Amer. Math. Soc., 1950, vol. 1, pp. 32–34.