A Strong Maximum Principle for Weakly L-Subharmonic Functions Walter Littman Indiana University Mathematics Journal 1959 text pdf 10.1512/iumj.1959.8.58048 10.1512/iumj.1959.8.58048 en Indiana Univ. Math. J. 8 (1959) 761 - 770 state-of-the-art mathematics http://iumj.org/access/