On Bodies Achieving Extreme Values of the Critical Mach Number, I David GilbargMax Shiffman Indiana University Mathematics Journal 1954 text pdf 10.1512/iumj.1954.3.53010 10.1512/iumj.1954.3.53010 en Indiana Univ. Math. J. 3 (1954) 209 - 230 state-of-the-art mathematics http://iumj.org/access/