On the Neumann Problem for Schroedinger Operators in Lipschitz Domains Zhongwei Shen Indiana University Mathematics Journal 1994 text pdf 10.1512/iumj.1994.43.43007 10.1512/iumj.1994.43.43007 en Indiana Univ. Math. J. 43 (1994) 143 - 176 state-of-the-art mathematics http://iumj.org/access/