Conformal Metrics in R^2 with Prescribed Curvature D. Sattinger Indiana University Mathematics Journal 1973 text pdf 10.1512/iumj.1973.22.22001 10.1512/iumj.1973.22.22001 en Indiana Univ. Math. J. 22 (1973) 1 - 4 state-of-the-art mathematics http://iumj.org/access/