Recently the present author developed a diagram formalism applicable to the de­ generate Bose fluids. The present author and Hara applied the formalism to show that the long distance 1/r and 1/r 2 behaviors of the pair distribution function are exactly cancelled for interacting Bose fluids. The basic ideas of the formalism have been given in separate articles. It is the purpose of the present article to present the formalism in a unified form. The formalism is developed in the canonical ensemble. However the generating function is used. Hence a criterion of the equivalence of the canonical and grand canonical ensembles is given and used in the discussions. Replace­