The Free Boundary Determined by the Solution to a Differential Equation David Kinderlehrer Indiana University Mathematics Journal 1976 text pdf 10.1512/iumj.1976.25.25016 10.1512/iumj.1976.25.25016 en Indiana Univ. Math. J. 25 (1976) 195 - 208 state-of-the-art mathematics http://iumj.org/access/