  We present an experimental study of the dynamics of holes in the valence
bands of 0, 1, and 2 dimensional undoped model cuprates, as expressed via the
screening of a Cu 2p core hole. The response depends strongly upon the
dimensionality and the details of the Cu-O-Cu network geometry and clearly goes
beyond the present theoretical state-of-the-art description within the
three-band d-p model.
