  We extend the Mori-Zwanzig equations to the case where the Liouvillian is
time-dependent by way of a Dyson identity due to Holian and Evans. This
extension makes it possible to treat, for example, more general cases of
continuous-wave (cw) or pulsed irradiation in NMR and coherent optics. The
formalism immediately allows for reference frame changes and approximations
based on coherent averaging.
