A Comparison and Fatou Theorem for a Class of Nondivergence Elliptic Equations with Singular Lower Order Terms Tomeu Barcelo Indiana University Mathematics Journal 1994 text pdf 10.1512/iumj.1994.43.43001 10.1512/iumj.1994.43.43001 en Indiana Univ. Math. J. 43 (1994) 1 - 24 state-of-the-art mathematics http://iumj.org/access/