Existence Theorems for Some Hydrodynamical Free Boundary Problems James Serrin, Jr. Indiana University Mathematics Journal 1952 text pdf 10.1512/iumj.1952.1.51001 10.1512/iumj.1952.1.51001 en Indiana Univ. Math. J. 1 (1952) 1 - 48 state-of-the-art mathematics http://iumj.org/access/