1. [1] H. Bass, J. Milnor, and J.-P. Serre, Solution of the congruence subgroup problem for ${\rm SL}\sb{n}\,(n\geq 3)$ and ${\rm Sp}\sb{2n}\,(n\geq 2)$, Inst. Hautes Études Sci. Publ. Math. (1967), no. 33, 59–137.
2. [2] D. Bump, Automorphic forms on ${\rm GL}(3,{\bf R})$, Lecture Notes in Mathematics, vol. 1083, Springer-Verlag, Berlin, 1984.
3. [3] D. Bump, S. Friedberg, and J. Hoffstein, Some cubic exponential sums, Preprint.
4. [4] D. Bump and J. Hoffstein, Cubic metaplectic forms on ${\rm GL}(3)$, Invent. Math. 84 (1986), no. 3, 481–505.
5. [5] S. Friedberg, A global approach to the Rankin-Selberg convolution for $\mathrm {SL}(3,\mathbb {Z})$, Preprint.