Schlicht Functions and Linear Differential Equations of Second Order Choy-Tak Taam Indiana University Mathematics Journal 1955 text pdf 10.1512/iumj.1955.4.54013 10.1512/iumj.1955.4.54013 en Indiana Univ. Math. J. 4 (1955) 467 - 480 state-of-the-art mathematics http://iumj.org/access/