1. R. von Mises and M. Schiffer: On Bergman’s integration method in two-dimensional compressible fluid flow. Advances in Applied Mechanics, Vol.1. New York: Academic Press Inc. (1948).
2. S. Bergman: The hodograph method in the theory of compressible fluids. Supplement to „Fluid Dynamics“ by R. v. Mises und K. O. Friedrichs, Brown University (1941-1942).
3. S. Bergman: Two-dimensional transonic flow patterns. Amer. J. Math. 70, pp. 856–891 (1948).
4. F. Tricomi: Sulle equazioni lineari alle derivato parziali di 2° ordine di tipo misto. Atti R. Accad. Naz. Linzei, Mem. délia Cl. Sci. Fis. Mat. e. Nat., Ser. 5, Vol. 14, 133-247 (1923).
5. F. I. Frankl: On the problems of Chaplygin for mixed sub-and supersonic flows. Bull. Acad. Sci. URSS, 8, 195–245 (1944) (in Russian).