Variational determination of multi-time Green's functions for degenerate Boze-systems and common structure of their hydrodynamical asymptotics

Variational determination of $n$-time ($n=2,3,\dots$) Green's functions for degenerate boze-systems is given. Basing on Bogolubov's ideas about reduction in the description of nonequilibrium states the mathymatical method for studing hydrodynamical asymptotics of multi-time Green's functions is developed. The resonance excitement diagrams of the first sound are investigated.