  A general approach for derivation of the spectral relations for the multitime
correlation functions is presented. A special attention is paid to the
consideration of the non-ergodic (conserving) contributions and it is shown
that such contributions can be treated in a rigorous way using multitime
temperature Green functions. Representation of the multitime Green functions in
terms of the spectral densities and solution of the reverse problem -- finding
of the spectral densities from the known Green functions are given for the case
of the three-time correlation functions.
