Maximum Principles for Degenerate Elliptic-Parabolic Operators Kazuo Amano Indiana University Mathematics Journal 1979 text pdf 10.1512/iumj.1979.28.28038 10.1512/iumj.1979.28.28038 en Indiana Univ. Math. J. 28 (1979) 545 - 557 state-of-the-art mathematics http://iumj.org/access/