The Differential Equations of the Stream Lines for Compressible Gas Flow B. BernsteinT. Thomas Indiana University Mathematics Journal 1955 text pdf 10.1512/iumj.1955.4.54026 10.1512/iumj.1955.4.54026 en Indiana Univ. Math. J. 4 (1955) 703 - 719 state-of-the-art mathematics http://iumj.org/access/