Remarks on Stefan-Type Free Boundary Problems for Parabolic Equations Avner Friedman Indiana University Mathematics Journal 1960 text pdf 10.1512/iumj.1960.9.59053 10.1512/iumj.1960.9.59053 en Indiana Univ. Math. J. 9 (1960) 885 - 903 state-of-the-art mathematics http://iumj.org/access/