Weak lensing "post-Born" effects are equivalent to pure lens-lens
  couplings
  We show that the so-called "post-Born" effects of weak lensing at 4th order
are equivalent to lens-lens couplings in the Born Approximation. We demonstrate
this by explicitly showing the equivalence of the canonical weak lensing
approach at 4th order using the anisotropy remapping method, to that of the 4th
order calculation of the lens-lens coupling effects using the Boltzmann
equation approach that was first developed in [Phys. Rev. D89, 123006].
Furthermore, we argue that to incorporate true "post-Born" effects, i.e. taking
into account non-straight photon paths, require the addition of a photon
deflection term which has not been taken into account in the canonical
formalism nor the Boltzmann method.
