The Perron-Wiener Method for Diffusion Operators L. Helms Indiana University Mathematics Journal 1963 text pdf 10.1512/iumj.1963.12.12061 10.1512/iumj.1963.12.12061 en Indiana Univ. Math. J. 12 (1963) 881 - 888 state-of-the-art mathematics http://iumj.org/access/