Gaussian Sums Over GL(2, Z/N) and Hecke Operators I Roy Fuller Indiana University Mathematics Journal 1975 text pdf 10.1512/iumj.1975.24.24042 10.1512/iumj.1975.24.24042 en Indiana Univ. Math. J. 24 (1975) 577 - 583 state-of-the-art mathematics http://iumj.org/access/