  We discuss possible choices for boundary conditions in the AdS/CFT
correspondence, and calculate the renormalisation group flow induced by a
double-trace perturbation. In running from the UV to the IR there is a unit
shift in the central charge. The discrepancy between our result and results
obtained by other authors is accounted for by the discovery that there is a
non-trivial flow for perturbations induced by bulk fields with masses
saturating the Breitenlohner-Freedman bound.
