Free Boundary Problems for Parabolic Equations I. Melting of Solids Avner Friedman Indiana University Mathematics Journal 1959 text pdf 10.1512/iumj.1959.8.58036 10.1512/iumj.1959.8.58036 en Indiana Univ. Math. J. 8 (1959) 499 - 517 state-of-the-art mathematics http://iumj.org/access/