Approximation of Fuchsian Groups and Automorphic Forms of Dimension 2 . T. MetzgerK. Rajeswara Rao Indiana University Mathematics Journal 1972 text pdf 10.1512/iumj.1972.21.21075 10.1512/iumj.1972.21.21075 en Indiana Univ. Math. J. 21 (1972) 937 - 949 state-of-the-art mathematics http://iumj.org/access/