Fundamentals of Reaction Theory: reaction rate constant in the statistical ensemble

filippo

I am reading some notes and I can't understand a specif bit:
the expression of the constant k_RP (RP means Reagents->Product) is as follows (Ξ is the heavyside function and C(t) the conditional probability):
k_RP=dC(t)/dt=<Ξ_R[0]*(dΞ_P[t]/dt)>/<Ξ_R[0]>
then for the following identity:
<A(t)A(t')>=<A(0)A(t-t')>=<A(t-t')A(0)>
at the numerator of the l.h.s. of k_RP's equation, we get
<Ξ_R[0]*(dΞ_P[t]/dt)>=-<(Ξ_R[0]/dt)*dΞ_P[t]>.
What identity is that one? I have no idea where it comes from...