On the Singularities of Solutions of Differential Equations of the Elliptic Type E. Netanyahu Indiana University Mathematics Journal 1954 text pdf 10.1512/iumj.1954.3.53037 10.1512/iumj.1954.3.53037 en Indiana Univ. Math. J. 3 (1954) 755 - 761 state-of-the-art mathematics http://iumj.org/access/