  Local cubic vertex functions of three higher even spin fields on AdS_D are
constructed from the Green function of three conserved currents that are dual
to the higher spin fields. Conservation of the currents implies lowest order
gauge invariance. These vertex functions appear by the UV divergence as the
residue of the highest order pole in the dimensional regularization parameter
\epsilon. The method works for even D and maintains covariance at any step. The
resulting formula is quite concise.
