A Uniqueness Proof for a Transonic Flow Problem L. Cook Indiana University Mathematics Journal 1978 text pdf 10.1512/iumj.1978.27.27005 10.1512/iumj.1978.27.27005 en Indiana Univ. Math. J. 27 (1978) 51 - 71 state-of-the-art mathematics http://iumj.org/access/