1. Aziz, A. K., Leventhal, S.: Optimal error estimates for least square methods. SINUM (submitted)
2. Aziz, A.K., Leventhal, S.: Equations of elliptic-hyperbolic type. In: Numerical solution of partial differential equations, Vol. III (B. Hubbard ed.), New York: Academic Press 1976
3. Fix, G.: A mixed finite element scheme for transonic flows. NASA-ICASE Report 76-25, 1976
4. Friedrichs, K.O.: Symmetric positive differential equations. Commun. pure appl. Math.11, 333?418 (1958)
5. Guderley, M.: The theory of transonic flows. Reading: Addison-Wesley 1962