Conservation Laws in Compressible Fluid Flow and Associated Mappings Charles Loewner Indiana University Mathematics Journal 1953 text pdf 10.1512/iumj.1953.2.52026 10.1512/iumj.1953.2.52026 en Indiana Univ. Math. J. 2 (1953) 537 - 561 state-of-the-art mathematics http://iumj.org/access/