  The coherent meson scattering off heavy nuclei with the production of two
particles in the final state is investigated. We obtain the form factors for
the direct production of the final state and through intermediate particles,
unstable ones that can decay inside the nucleus and virtual ones. The cases of
scattering both in the Coulomb and in the strong field of the nucleus are
considered. This work is stimulated by an experimental study of the chiral
anomaly in a beam of charged kaons in the OKA facility.
