“…If ϕ is an eigenfunction of the Hecke algebra (see [ 17 , Sect. 6.4]), we define its L -function by L ( ϕ , s ):=∑ m A ϕ (1, m ) m − s , and the Rankin–Selberg L -function by It follows from [ 25 , Theorem 2] or [ 6 , Corollary 2] that the coefficients are essentially bounded on average, uniformly in ν : The space of cusp forms is equipped with an inner product It is known that can be continued holomorphically to ℂ with the exception of a simple pole at s =1 whose residue is proportional to ∥ ϕ ∥ 2 [ 17 , Theorem 7.4.9]. The proportionality constant is given in the next lemma.…”