Suppose we have a bipartite quantum system which is preapared in some state, say, at t = 0 (preselection) and postselected at a later time, say, t = T. The correlations between two parts of the bipartite system at intermediate times (0> t > T) must depend on the initial and final states according to my understanding. The correlations between parts of the bipartite system with only the initial state is known. Due to time reversal symmetry, similarly correlations can be defined, if only the final state is fixed. But how to define/describe the correlation for a system, which is both pre and postselected?