Monge-Ampere Functions, I Joseph Fu Indiana University Mathematics Journal 1989 text pdf 10.1512/iumj.1989.38.38035 10.1512/iumj.1989.38.38035 en Indiana Univ. Math. J. 38 (1989) 745 - 771 state-of-the-art mathematics http://iumj.org/access/