  We carefully examine all the four derivations of the renormalization group
equation (RGE) for the so-called $\Vlk$ potential, given by Bogner, \textit{et.
al.}[nucl-th/0111042]. Two derivations based on the ``semi-group composition
law'' are shown to be unjustified, while the other two based on the
completeness relation of the model space must be modified if there are bound
states. It is however shown that the RGE is unchanged if the bound state
wavefunctions in the reduced theory are required to have the same low-momentum
components as those in the original theory. Several aspects of the $\Vlk$
approach are also discussed.
