Formal solutions for response functions of superconductors and 3He(B). I

The superfluid Fermi liquids with BCS and BW pairing are considered in the collisionless regime and with the effective quasiparticle interaction in the pairing channel, restricted to only one Legendre harmonic. In such a case, the density-density, density-current and current-current correlation functions are expressed in terms of matrix elements of some scalar operator and the gauge invariance of such expressions is proved. The expressions obtained for autocorrelation functions are discussed and some of their limiting values are established.