 To put (RC) to use, it is important to notice that the equations defining the various levels of EH above can be written in terms of correlations. Taking into account that we are dealing with discrete systems (and hence we have \(T_{t_1\rightarrow t}B = T_k B\) where \(k\) is the number of time steps it takes to get from \(t_1\) and \(t)\), these equations read: