A Problem in Hydraulics with Non-Monotone Free Boundary Avner Friedman Indiana University Mathematics Journal 1976 text pdf 10.1512/iumj.1976.25.25046 10.1512/iumj.1976.25.25046 en Indiana Univ. Math. J. 25 (1976) 577 - 592 state-of-the-art mathematics http://iumj.org/access/