A note on the mean value of the zeta and L-functions. XIV
  The aim of the present note is to develop a study on the feasibility of a unified theory of mean values of automorphic L-functions, a desideratum in the field. This is an outcome of the investigation commenced with Part XII of this series, where a framework was laid on the basis of the theory of automorphic representations, and a general approach to the mean values was envisaged. Specifically, it is shown here that the inner-product method, which was initiated by A. Good and greatly enhanced by M. Jutila, ought to be brought to perfection so that the mean square of the L-function attached to any cusp form on the upper half-plane could be reached within the notion of automorphy. The Kirillov map is our key implement. Because of its geometric nature, our argument appears to extend to bigger linear Lie groups. This paper is essentially self-contained. 
Yoichi Motohashi