  We show that the usual expression for evaluating electron-phonon coupling and
the phonon linewidth in 2D metals with a cylindrical Fermi surface cannot be
applied near the wave vector corresponding to the Kohn singularity. Instead,
the Dyson equation for phonons has to be solved self-consistently. If a
self-consistent procedure is properly followed, there is no divergency in
either the coupling constant or the phonon linewidth near the offending wave
vectors, in contrast to the standard expression.
