1. D. Atkin, J. Lehner. Hecke operators on Γ0(m). Math. Ann.
185 (1970), 134–260.
2. J. Deshouillers, H. Iwaniec. Rankin-Selberg ζ functions in the Selberg trace formula and related topics. Contemporary Math., Amer. Math. Soc.
53 (1983).
3. J. Huntley. Multiplicity one theorems for automorphic forms. Ph.D. Thesis, Stanford Univ., 1987.
4. J. Huntley. Spectral multiplicity on products of hyperbolic spaces. Preprint.
5. H. Jacquet, R. Langlands. Automorphic forms on GL
2. Lecture Notes Math, Springer-Verlag, New York, 1970.